Beat: Allow setting beat name in configuration

[marclop]

Motivation/summary

Uses the beat name if set in the configuration file. Restores what used to work on 7.x and perhaps prior to #9149 being introduced.

Checklist

• Update CHANGELOG.asciidoc
  - [ ] Update package changelog.yml (only if changes to apmpackage have been made)
  - [ ] Documentation has been updated

How to test these changes

1. Set name: my-apm-server under the APM config in testing/infra/k8s/base/stack/apm-server.yaml
2. Tilt up
3. Navigate to Stack Monitoring -> Verify that APM Server instance is named my-apm-server.

[mergify]

This pull request does not have a backport label. Could you fix it @marclop? 🙏
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.

NOTE: backport-skip has been added to this pull request.

[marclop]

Seems like the system tests are failing because of GeoIP changes, which are unrelated to this PR.

[mergify]

This pull request does not have a backport label. Could you fix it @marclop? 🙏
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.

NOTE: backport-skip has been added to this pull request.

[carsonip]

@marclop this is currently not in 8.12 branch. We'll have to either remove the v8.12.0 tag on this PR or backport this fix to 8.12 and update changelogs.

Alternatively, backport to 8.12.1

[marclop]

Thanks for the ping. I think it'd be good to ship this on 8.12.0. I'll add the backport labels. They weren't available a few days ago.

[simitt]

Tested with BC-2:
changed following in apm-server.yml

name: mytest-apm-server
http.enabled: true

Then started the apm-server and running curl -i -k localhost:5066 returns

{ .. "name":"mytest-apm-server" .. }