Autodiscover memleak

[rsafonseca]

Proposed commit message

Fix memory leak in autodiscovery
Before this change, start events were never removed from memory due to a permanent reference to mapstr.Clone() object containing the full event
After this change, the event is freed from memory as soon as handle_start finishes, maintaining only the metadata of the even in memory
After a stop event, all existing references to the metadata of the stopped config are now removed from the autodiscover meta map

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Screenshots

Logs

[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @rsafonseca? 🙏.
For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

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

[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 and remove the backport-8.x label.

[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)

[rsafonseca]

This is tested in a production environment and the leak seems completely resolved :)
It's been running for >24h without any errors or leaks

[rsafonseca]

for seeing the change over the past few versions, compared with v8.16.0-wls.2 which contains the fix