[Security Assistant] V2 Knowledge Base Settings feedback and fixes

[spong]

Summary

This PR is a follow up to #192665 and addresses a bunch of feedback and fixes including:

• Adds support for updating/editing entries
• Fixes initial loading experience of the KB Settings Setup/Table
• Fixes two bugs where semantic_text and text must be declared for IndexEntries to work

TODO:

• Add support for required entries in initial prompt
• Add suggestions to index and fields inputs
• Add new Settings Context Menu items for KB and Alerts
• Adds URL deeplinking to securityAssistantManagement
• Fix bug where updating entry does not re-create embeddings
• Fix loading indicators when adding/editing entries
• API integration tests for update API

Checklist

Delete any items that are not applicable to this PR.

• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• Documentation was added for features that require explanation or tutorials
  • Docs being tracked in [Request] 8.16 Security Assistant Custom Knowledge Bases security-docs#5337 for when feature flag is enabled
• Unit or functional tests were updated or added to match the most common scenarios

[elasticmachine]

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