[Security Solution][AI Assistant] Update Message schema and interface (#13657)

[e40pud]

Summary

Epic: https://github.com/elastic/security-team/issues/12768
Meta: https://github.com/elastic/security-team/issues/13657
RFC: internal link

With these changes we update the conversation Message schema by adding a new field id. This will allow us to easily refer messages that are summarized.

New messages

All new messages will be added with the id field set.

Existing messages

The id field for all existing messages will be undefined and will be updated whenever a user updates the conversation:

• appends new messages
• regenerates a last assistant respond

In those case above, all messages within the ongoing conversation will be updated and will have a id field set.

Testing scenarios

1. Existing messages without id

• Create conversation with messages in "pre this PR" code (e.g. main branch)
• Checkout code from this PR
• Check via Dev Tools that messages within the conversations index do not have id field set
• Add a new message to one of the conversations
• Check that all messages within that conversation are updated and id field set for all of them

2. New messages

• Checkout code from this PR
• Create a new chat and add new messages
• Check via Dev Tools that all messages within the new conversation have id field set

[elasticmachine]

Pinging @elastic/security-solution (Team: SecuritySolution)

[e40pud]

/ci

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: c6d3696

Metrics [docs]

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
securitySolution	10.4MB	10.4MB	+20.0B

History

• 💔 Build #331283 failed f362044
• 💔 Build #331252 failed f362044
• 💔 Build #331213 failed 86135c7

cc @e40pud