Add a nightly build of all examples to GitHub Actions

[mairas]

With PR #296, the CI checks run for each PR are only a subset of all examples. To ensure that every example is in working order, every example should be built as part of a nightly CI run.

Things to consider:

• To preserve resources, the nightly tests should only run on the SignalK/SensESP repository and not on any forks
• To avoid manually maintaining a list of examples to be built, we should detect the examples with globbing (wildcards)