Set transaction type only if unset

[kelunik]

What does this PR do?

This PR avoids overwriting a custom transaction type if set by the application.

Currently, changing the transaction type in an application has no effect, because it is changed by ServletTransactionHelper again.

Separating transaction types is necessary if you want to separate main requests from internal RPC requests for example.

Checklist

• This is an enhancement of existing features, or a new feature in existing plugins
  • I have updated CHANGELOG.asciidoc
  • I have added tests that prove my fix is effective or that my feature works
  • Added an API method or config option? Document in which version this will be introduced
  • I have made corresponding changes to the documentation
• This is a bugfix
  • I have updated CHANGELOG.asciidoc
  • I have added tests that would fail without this fix
• This is a new plugin
  • I have updated CHANGELOG.asciidoc
  • My code follows the style guidelines of this project
  • I have made corresponding changes to the documentation
  • I have added tests that prove my fix is effective or that my feature works
  • New and existing unit tests pass locally with my changes
  • I have updated supported-technologies.asciidoc
  • Added an API method or config option? Document in which version this will be introduced
  • Added an instrumentation plugin? Describe how you made sure that old, non-supported versions are not instrumented by accident.
• This is something else
  • I have updated CHANGELOG.asciidoc

[cla-checker-service]

💚 CLA has been signed

[github-actions]

👋 @kelunik Thanks a lot for your contribution!

It may take some time before we review a PR, so even if you don’t see activity for some time, it does not mean that we have forgotten about it.

Every once in a while we go through a process of prioritization, after which we are focussing on the tasks that were planned for the upcoming milestone. The prioritization status is typically reflected through the PR labels. It could be pending triage, a candidate for a future milestone, or have a target milestone set to it.

[JonasKunz]

Thanks for your contribution!
It indeed does make sense to allow overriding the transaction type.
I've added a testcase proving your fix works as desired and added a changelog for you.

Could you please sign the CLA so that we can merge this PR?

[kelunik]

Hey @JonasKunz,

Thanks for the review and test! I have the CLA on my list, unfortunately it needs to go through legal before I can submit it.

[JonasKunz]

run elasticsearch-ci/docs

[JonasKunz]

run elasticsearch-ci/docs

[JonasKunz]

Thanks for your contribution @kelunik !

[jackshirazi]

approved

[kelunik]

@JonasKunz Thank you for the tests and handling with the CLA!