[Logs / Metrics UI] NP followups [Meta issue]

[Kerry350]

Summary

This is a meta ticket for tracking all followups for the metrics / logs apps after the NP migration.

They are ranked (roughly) in the order we should address them.

High

• Make sure application links don't cause a page reload ([Logs / Metrics UI] [NP followup] Make sure application links don't cause a page reload #58007)

Medium

• Cleanup link-to routes ([Logs / Metrics UI] [NP followup] Cleanup link-to routes #58005)
• Fix navigation within the same app via the Kibana nav bar ([Logs / Metrics UI] [NP followup] Fix navigation within the same app via the Kibana nav bar #58112)
• Remove the uses of legacy_singletons ([Logs UI] [NP followup] Remove legacy_singletons uses #58001)
• Only use plugin start contracts in the UI ([Logs / Metrics UI] [NP followup] Only use plugin start contracts in the UI #58014)
• Review index.scss styles ([Logs / Metrics UI] [NP followup] Review index.scss styles #58114)

Low

• Discuss / amend shared Observability hooks ([Logs / Metrics UI] [NP followup] Discuss / amend shared Observability hooks #58018)
• Remove the legacy plugin index.ts ([Logs / Metrics UI] [NP followup] Remove the legacy plugin #57999)
• Cleanup /common ([Logs / Metrics UI] [NP followup] Cleanup /common #58002)
• Add context menu functional tests back ([Logs / Metrics UI] [NP followup] Add functional tests back #58012)
• Support Observable nature of config ([Logs / Metrics UI] [NP followup] Make config handling reactive #59147)

[elasticmachine]

Pinging @elastic/logs-metrics-ui (Team:logs-metrics-ui)