feat: return an error if tbs config fails

[kruskall]

Motivation/summary

failure to process the tbs config will log a message and silently fallback to the default config with tbs disabled.
This is not ideal and doesn't match the behaviour of other configs which return an error to the caller.

Update the tbs config logic to return an error if processing fails

Update test to assert error on malformed configs

We might need to be careful with backporting (maybe only 9.x ?)

Checklist

• Update CHANGELOG.asciidoc
• Documentation has been updated

For functional changes, consider:

• Is it observable through the addition of either logging or metrics?
• Is its use being published in telemetry to enable product improvement?
• Have system tests been added to avoid regression?

How to test these changes

• start apm-server with malformed tbs config
• observe a failure

Related issues

[github-actions]

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[mergify]

This pull request does not have a backport label. Could you fix it @kruskall? 🙏
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-9./d is the label to automatically backport to the 9./d branch. /d is the digit.
• backport-active-all is the label that automatically backports to all active branches.
• backport-active-8 is the label that automatically backports to all active minor branches for the 8 major.
• backport-active-9 is the label that automatically backports to all active minor branches for the 9 major.