Run Airflow package preparation in docker in breeze/CI (apache#15723)

Moved building airflow package to within the container similarly
as we do with provider packages. This has the following advantages:

* common environment used to build airflow
* protection against leaking SECRET_* variables in CI in case third
  party packages are installed
* specify --version-suffixes and renaming the packages according
  to destination (SVN/PyPI) automatically
* no need to have node installed in CI runner
* no need to have node installed in DockerHub
* no need to install PIP/Python3 in DockerHub runner (currently
  Python2 is still default and it fails the build there)
* always deleting egg-info and build before the build
* cleaning up egg-info and build after the build

Also following the way providers are released, the documentation
is updated to change publishing Airflow using previously voted
and renamed packages - the very same packages that were committed
to SVN. This way anyone will be able to manually verify that the
packages in SVN are the same as those published in SVN and there
is no need to rebuild the packages when releasing them.

Prepares provider release after PIP 21 compatibility (apache#15576)

This PR updates changelog and bumps version of providers to be
released after we reached PIP 21 compatibility. It is necessary
for two reasons:

1) We need it in order to get constraints for PyPI released
   providers to be updated automatically (PIP 21 conflicts master
   airflow with few released providers

2) We want to release Airflow 2.0.3 which will be PIP 21 installable
   with those providers.

Prepares provider release after PIP 21 compatibility (apache#15576)

This PR updates changelog and bumps version of providers to be
released after we reached PIP 21 compatibility. It is necessary
for two reasons:

1) We need it in order to get constraints for PyPI released
   providers to be updated automatically (PIP 21 conflicts master
   airflow with few released providers

2) We want to release Airflow 2.0.3 which will be PIP 21 installable
   with those providers.

Prepares provider release after PIP 21 compatibility (apache#15576)

This PR updates changelog and bumps version of providers to be
released after we reached PIP 21 compatibility. It is necessary
for two reasons:

1) We need it in order to get constraints for PyPI released
   providers to be updated automatically (PIP 21 conflicts master
   airflow with few released providers

2) We want to release Airflow 2.0.3 which will be PIP 21 installable
   with those providers.

Prepares provider release after PIP 21 compatibility (apache#15576)

This PR updates changelog and bumps version of providers to be
released after we reached PIP 21 compatibility. It is necessary
for two reasons:

1) We need it in order to get constraints for PyPI released
   providers to be updated automatically (PIP 21 conflicts master
   airflow with few released providers

2) We want to release Airflow 2.0.3 which will be PIP 21 installable
   with those providers.

Prepares provider release after PIP 21 compatibility (apache#15576)

This PR updates changelog and bumps version of providers to be
released after we reached PIP 21 compatibility. It is necessary
for two reasons:

1) We need it in order to get constraints for PyPI released
   providers to be updated automatically (PIP 21 conflicts master
   airflow with few released providers

2) We want to release Airflow 2.0.3 which will be PIP 21 installable
   with those providers.

Prepares provider release after PIP 21 compatibility (apache#15576)

This PR updates changelog and bumps version of providers to be
released after we reached PIP 21 compatibility. It is necessary
for two reasons:

1) We need it in order to get constraints for PyPI released
   providers to be updated automatically (PIP 21 conflicts master
   airflow with few released providers

2) We want to release Airflow 2.0.3 which will be PIP 21 installable
   with those providers.

Prepares provider release after PIP 21 compatibility (apache#15576)

This PR updates changelog and bumps version of providers to be
released after we reached PIP 21 compatibility. It is necessary
for two reasons:

1) We need it in order to get constraints for PyPI released
   providers to be updated automatically (PIP 21 conflicts master
   airflow with few released providers

2) We want to release Airflow 2.0.3 which will be PIP 21 installable
   with those providers.

Prepares provider release after PIP 21 compatibility (apache#15576)

This PR updates changelog and bumps version of providers to be
released after we reached PIP 21 compatibility. It is necessary
for two reasons:

1) We need it in order to get constraints for PyPI released
   providers to be updated automatically (PIP 21 conflicts master
   airflow with few released providers

2) We want to release Airflow 2.0.3 which will be PIP 21 installable
   with those providers.

Prepares provider release after PIP 21 compatibility (apache#15576)

This PR updates changelog and bumps version of providers to be
released after we reached PIP 21 compatibility. It is necessary
for two reasons:

1) We need it in order to get constraints for PyPI released
   providers to be updated automatically (PIP 21 conflicts master
   airflow with few released providers

2) We want to release Airflow 2.0.3 which will be PIP 21 installable
   with those providers.