Ground rules on adding new schema

Brand new schema, particularly when written specifically for IPA, should be
added in share/*.ldif. Any new files need to be explicitly loaded in
ipaserver/install/dsinstance.py. These simply get copied directly into
the new instance schema directory.

Existing schema (e.g. in an LDAP draft) may either be added as a separate
ldif in share or as an update in the updates directory. The advantage of
adding the schema as an update is if 389-ds ever adds the schema then the
installation won't fail due to existing schema failing to load during
bootstrap.

If the new schema requires a new container then this should be added
to install/bootstrap-template.ldif.