[8.x](backport #41795) Add registry to Filebeat's diagnostic

[mergify]

Proposed commit message

This commit adds Filebeat's registry folder to the Elastic-Agent
diagnostics. It's called registry.tar.gz and includes all registry files
on ${path.home}/registry.

The registry is first archived into a temporary tar file. The
temporary file is created by calling os.CreateTemp and will use the
OS's temporary folder. Then it's gziped in memory and returned to
Elastic-Agent, finally the temporary file is removed from the disk.

If the final gziped file is more than 20mb, it is skipped due to its large
size.

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.

Disruptive User Impact

None.

Author's Checklist

How to test this PR locally

The easiest way to test it locally is to package the Elastic-Agent with your local build of Beats by setting EXTERNAL=false when calling mage build in the Elastic-Agent folder.

Then, deploy the Elastic-Agent, let it ingest some logs and request the diagnostics. Extract the diagnostics and look for registry.tar.gz in components/filestram-* folders.

You can also run the integration tests:

go test -tags integration -count=1 -run=TestEmptyegistryIsInDiagnostics -v ./tests/integration
go test -tags integration -count=1 -run=TestFilestreamRegistryIsInDiagnostics -v ./tests/integration

Related issues

• Closes Add Filebeat registry to the diagnostics bundle for the control V2 protocol #33238

## Use cases
## Screenshots

Logs

Full log entries

{"log.level":"debug","@timestamp":"2024-11-27T11:00:35.812-0500","log.logger":"diagnostics","log.origin":{"function":"github.com/elastic/beats/v7/filebeat/beater.gzipRegistry","file.name":"beater/diagnostics.go","file.line":54},"message":"temporary file '/tmp/filebeat-registry-640175774.tar' created","service.name":"filebeat","ecs.version":"1.6.0"}
{"log.level":"debug","@timestamp":"2024-11-27T11:00:35.812-0500","log.logger":"diagnostics","log.origin":{"function":"github.com/elastic/beats/v7/filebeat/beater.tarFolder","file.name":"beater/diagnostics.go","file.line":116},"message":"starting to walk '/home/tiago/devel/beats/x-pack/filebeat/build/integration-tests/TestRegistryIsInDiagnostics3276586231/data/registry'","service.name":"filebeat","ecs.version":"1.6.0"}
{"log.level":"debug","@timestamp":"2024-11-27T11:00:35.812-0500","log.logger":"diagnostics","log.origin":{"function":"github.com/elastic/beats/v7/filebeat/beater.tarFolder.func1","file.name":"beater/diagnostics.go","file.line":140},"message":"adding '/home/tiago/devel/beats/x-pack/filebeat/build/integration-tests/TestRegistryIsInDiagnostics3276586231/data/registry/filebeat/log.json' to the tar archive","service.name":"filebeat","ecs.version":"1.6.0"}
{"log.level":"debug","@timestamp":"2024-11-27T11:00:35.812-0500","log.logger":"diagnostics","log.origin":{"function":"github.com/elastic/beats/v7/filebeat/beater.tarFolder.func1","file.name":"beater/diagnostics.go","file.line":140},"message":"adding '/home/tiago/devel/beats/x-pack/filebeat/build/integration-tests/TestRegistryIsInDiagnostics3276586231/data/registry/filebeat/meta.json' to the tar archive","service.name":"filebeat","ecs.version":"1.6.0"}
{"log.level":"debug","@timestamp":"2024-11-27T11:00:35.812-0500","log.logger":"diagnostics","log.origin":{"function":"github.com/elastic/beats/v7/filebeat/beater.gzipRegistry","file.name":"beater/diagnostics.go","file.line":63},"message":"finished gziping Filebeat's registry","service.name":"filebeat","ecs.version":"1.6.0"}

Only the message field:

"temporary file '/tmp/filebeat-registry-640175774.tar' created"
"starting to walk '/home/tiago/devel/beats/x-pack/filebeat/build/integration-tests/TestRegistryIsInDiagnostics3276586231/data/registry'"
"adding '/home/tiago/devel/beats/x-pack/filebeat/build/integration-tests/TestRegistryIsInDiagnostics3276586231/data/registry/filebeat/log.json' to the tar archive"
"adding '/home/tiago/devel/beats/x-pack/filebeat/build/integration-tests/TestRegistryIsInDiagnostics3276586231/data/registry/filebeat/meta.json' to the tar archive"
"finished gziping Filebeat's registry"
```<hr>This is an automatic backport of pull request #41795 done by [Mergify](https://mergify.com).

[elasticmachine]

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