Improve description in automated PR from dependency-update.yml

[ArBridgeman]

Summary

The dependency-update.yml creates a PR that looks like: #790

We should augment the description provided so that contributors know which steps they need to take to:

1. trigger the CI
2. finalize the PR, e.g. what manual steps need to be done

We'd like this to be similar in nature to what project-keeper produces:
exasol/kafka-connector-extension#171

As #683 (worked on in #779), first adds the dependency-update.yml, it would be ideal if this is done before a new PTB release.

To Dos

Modify the documentation

Modify https://exasol.github.io/python-toolbox/main/user_guide/features/github_workflows/index.html#dependency-update:

• Use the RST option to display the schedule for running
• Write out a bit more how the pipeline works & what the user is expected to do (in vague wording)
• Handle this comment -> add dependency-update workflow template (fixes #683) #756 (comment)

Notes:

• It runs once weekly or on demand. If the criteria (has vulnerability, were changes) are met, then a PR is created & a slack notification sent.
• Users need to open the PR and perform some manual steps which are described in the PR description.
• See if PK has more in their documentation.

Modify the PR description

Modify exasol/toolbox/templates/github/workflows/dependency-update.yml

• Need to add parts similar in style to 🔐 Update dependencies to fix vulnerabilities kafka-connector-extension#171
• To simply run the CI, you can close and re-open the PR
• Manual steps we need to take include:
  • update the workflows with poetry run -- nox -s workflow:generate -- all -> bot cannot do
  • check if there are remaining vulnerabilities with poetry run -- nox -s dependency:audit and try to fix if there's a fix version. If it's not easy and there is a known fix, create an issue to look into later.
  • update the changelog -> add an entry that the poetry.lock was updated to resolve vulnerabilities. Maybe note that the release:prepare will write out the specifics later 😉
• Propagate changes to the .github/workflows/dependency-update.yml