docs(apm-server): update golang version in version.asciidoc

[v1v]

What

Update the Golang version when the version has been updated in https://github.com/elastic/apm-server/blob/main/.go-version.

Notify the APM-server team when changes need to be reviewed... However, we could automate the merge since those changes already exist in the main branch.

Why

elastic/apm-server#12412 caused it since elastic/apm-server#12341 moved the version.asciidoc in this repository.

Question

This is only supported for the main branch, so we might need to support the same for the existing active release branches. I'd like to discuss this in a follow-up.

[mergify]

This pull request does not have a backport label. Could you fix it @v1v? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-/d./d is the label to automatically backport to the /d./d branch. /d is the digit
  NOTE: backport-skip has been added to this pull request.

[bmorelli25]

Thanks, @v1v. We didn't consider this when moving the docs from elastic/apm-server to elastic/observability-docs. I appreciate you looking out!

Question: Why do we need to maintain this variable in the documentation? AFAICT, we set the :go-version: in the version.asciidoc file but never actually use it anywhere in the docs.

EDIT: It looks like we don't use any of these version.asciidoc variables in the docs:

:go-version: 1.21.5
:python: 3.7
:docker: 1.12
:docker-compose: 1.11

Should we be?

[v1v]

Hey @bmorelli25 ,

Question: Why do we need to maintain this variable in the documentation?

No clue :/

EDIT: It looks like we don't use any of these version.asciidoc variables in the docs:

If so, then we don't need this PR, let's things to maintain that's even better 🙏

I'll close this PR now and then let you decide what to do with those variables. Thanks Brandon for your review

[bmorelli25]

Sounds good to me! I opened a follow-up PR to remove these attributes: #3554.