[Helm chart] Adjust Elastic Agent Helm Chart as ingesting GZIP file is GA on 9.3.0 #11559

Refactor the Elastic Agent Helm Chart account for ingesting GZIP files being GA and on by default on filebeat 9.3.0.

Acceptance Criteria

• Remove gzip_experimental from template.
• keep rotated log ingestion as opt-in
• If gzip_experimental is passed by a user in values.yaml during an upgrade, render it harmlessly or log a deprecation warning (via NOTES.txt?).

Corner Cases

Test a Helm upgrade from the previous version to 9.2.0 with custom values to ensure the release does not fail due to unknown config keys.