functionaltests: add 8.17 tests

[endorama]

Motivation/summary

Add 8.17 tests to functional tests:

1. a plain upgrade from 8.16 to 8.17
2. an upgrade using the reroute processor
3. an upgrade fromr 8.14, from the APM integration to the apm-data plugin.

Tests will be executed in parallel to keep the timeout to 30 minutes. This introduces code duplication in the Terraform code that will be addressed later on.

Checklist

How to test these changes

GitHub workflow functionaltests should be green.

Initial test run https://github.com/elastic/apm-server/actions/runs/12889138214 (failed)

Related issues

#14100

[mergify]

This pull request does not have a backport label. Could you fix it @endorama? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-7.17 is the label to automatically backport to the 7.17 branch.
• backport-8./d is the label to automatically backport to the 8./d branch. /d is the digit.
• backport-8.x is the label to automatically backport to the 8.x branch.

[mergify]

backport-8.x has been added to help with the transition to the new branch 8.x.
If you don't need it please use backport-skip label.

[endorama]

new test run: https://github.com/elastic/apm-server/actions/runs/12892896166

[mergify]

This pull request is now in conflicts. Could you fix it @endorama? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b 817functests upstream/817functests
git merge upstream/main
git push upstream 817functests