Add atomic alias updates for zero-downtime index swaps

[stevebauman]

Summary

• add an AliasActions builder for atomic alias additions, removals, and index retirement
• support is_write_index when creating and reading aliases
• expose atomic alias updates through the index manager
• make the fake index manager mirror alias replacement, deletion, and atomic update state
• document the blue-green index swap API

Why

The adapter previously exposed only separate alias creation and deletion calls. Applications rebuilding a physical index could not atomically move a stable alias from the old index to the new one, creating a possible gap during a blue-green cutover.

This adds a first-party abstraction over OpenSearch's atomic aliases API so higher-level packages can safely coordinate zero-downtime index deployments.

Developer impact

Existing putAlias() and deleteAlias() usage remains unchanged. Consumers can now designate an alias write index and compose a complete cutover:

$actions = (new AliasActions)
    ->remove('posts_blue', 'posts')
    ->add('posts_green', new Alias('posts', isWriteIndex: true));

$indices->updateAliases($actions);

Adding updateAliases() to IndexManagerInterface means custom third-party implementations of that interface must implement the new method.

Validation

• 168 unit tests passed with 283 assertions
• 3 live OpenSearch integration tests passed with 17 assertions
• Laravel Pint passed
• git diff --check passed