Add extension options for specific workflow templates in the PTB

[ArBridgeman]

Summary

Projects using the PTB workflow templates often try to extend workflows.

We've already added some extensions:

• merge-gate-extension.yml
• fast-tests-extension.yml
• cd-extension.yml

To Dos

• Perform a search to see what other extensions are needed
• Create a proposal and run it past @tkilias
• Create the additional workflow extensions and ensure proper test coverage
• Modify the documentation -> https://exasol.github.io/python-toolbox/main/user_guide/features/github_workflows/index.html#workflow-extensions

[ckunki]

Is this ticket already fixed by ?

• Allow extending GitHub workflow cd.yml #862

[ArBridgeman]

Is this ticket already fixed by ?

* [Allow extending GitHub workflow `cd.yml` #862](https://github.com/exasol/python-toolbox/pull/862)

No, if you look at the tasks, the goal is to identify other cases where an extension is needed. No such investigation was made. The cd-extension.yml was added because the ITDE needed it.

[ArBridgeman]

This was done in #862 and #425. If further extensions are needed, which is not anticipated at the moment, then they can be requested.