core/services/chainlink: normalize feature config

[jmank88]

The new MultiFeedsManagers feature flag came with an extra exceptional method for accessing indirectly via global config. This PR removes FeatureMultiFeedsManagers() and adjusts callers to use the standard pattern.

[github-actions]

I see you updated files related to core. Please run pnpm changeset in the root directory to add a changeset as well as in the text include at least one of the following tags:

• #added For any new functionality added.
• #breaking_change For any functionality that requires manual action for the node to boot.
• #bugfix For bug fixes.
• #changed For any change to the existing functionality.
• #db_update For any feature that introduces updates to database schema.
• #deprecation_notice For any upcoming deprecation functionality.
• #internal For changesets that need to be excluded from the final changelog.
• #nops For any feature that is NOP facing and needs to be in the official Release Notes for the release.
• #removed For any functionality/config that is removed.
• #updated For any functionality that is updated.
• #wip For any change that is not ready yet and external communication about it should be held off till it is feature complete.

🎖️ No JIRA issue number found in: PR title, commit message, or branch name. Please include the issue ID in one of these.

[cl-sonarqube-production]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube

[graham-chainlink]

Thanks for showing me the right way to inject the feature tag into the service!