[Fleet] Automate Update of Bundled Packages

[kpollich]

Ref #112095

In 8.1, we introduced support in Fleet for "bundled packages," which are fetched at build-time and bundled with the Kibana distributable. These packages are configured through a fleet_packages.json file at the top level of the Kibana repository.

Currently, any time a new version of one of these bundled packages is deployed and considered ready for release, we need to manually update its entry in fleet_packages.json to ensure we bundle the latest version of that package. This adds an additional, manual step to the package promotion process for these packages, and adds room for human error.

It'd be ideal to automate this process using Kibana CI to ensure fleet_packages.json stays up to date with the latest version of each package as served by the package registry. We also likely want these updates to go through a final review step, so proposing the updates to fleet_package.json via a PR labeled for appropriate code owner review would be ideal.

A few potential solutions could be:

1. A nightly job that queries EPR for each package in fleet_packages.json and updates the version accordingly via GitHub PR
2. Alter the existing build job to always fetch the latest version of packages from EPR
3. Update elastic-package CLI tooling or CI to also handle the update of fleet_packages.json via GitHub PR, see Add guidance for updating bundled packages in Kibana elastic-package#733

[elasticmachine]

Pinging @elastic/fleet (Feature:EPM)

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)

[kpollich]

cc @joshdover for any input on the proposed solutions and use cases above.