[Epic] Improve Spring App Configuration

[saragluna]

This is an epic including all Spring App Configuration related work:

• App config remove revisions #21696: App Config remove revisions
• [FEATURE REQ] Appconfig default-context for each store #15364: Appconfig default-context for each store
• App config integration tests #21840: Add integration tests for App Config
• Rename internal package structure to match new format.
• Rename cache-expiration configuration to refresh-interval
• Move Feature Flag refresh-interval to be under monitoring