feat(ai): add update conversation

[dbanksdesign]

Issue #, if available:

Description of changes:

Adds an update function on AI Conversations so users can update name and metadata fields of a conversation. Also adding those fields as optional params for create function.

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[changeset-bot]

🦋 Changeset detected

Latest commit: aa4c942

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@aws-amplify/data-schema	Minor

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[palpatim]

Recommend you mark this as Draft to ensure we don't accidentally merge it until its dependent PRs are released:

• feat(conversation): enable update mutations on conversation model amplify-category-api#2948
• feat: remove update: null for conversation model in MIS amplify-codegen#895

[iartemiev]

Changes LGTM overall.

I'd like to see integ test coverage (./packages/integration-tests/__tests__/defined-behavior/*) for the recent ai work e.g. update conversation, delete conversation. Can be part of a follow-up PR.