Feature Request: Bluesky Timeline Block

### Impacted plugin

Jetpack, Social

### What

Now that Jetpack includes a way for folks to connect their Bluesky account, it would be nice to use that connection to display posts from their Bluesky account on the site.

### How

Bluesky includes an API endpoint, `app.bsky.feed.getTimeline`, that can be used to fetch recent posts from a Bluesky timeline:
https://docs.bsky.app/docs/api/app-bsky-feed-get-timeline

I think it would be nice if we could leverage that API endpoint to introduce a new block that would display recent posts from a Bluesky timeline when we have an active Bluesky connection on the site. As an alternative and may be a better UX, the block could include a UI similar to the one built for Jetpack Social, allowing one to provide an application password and connect their Bluesky account to the block.

Review the existing Bluesky connection in Jetpack and Social, then read the app.bsky.feed.getTimeline API documentation linked in the issue. The work is complete when a new block displays recent posts for an active Bluesky connection, but the issue leaves the account-connection UX and implementation scope open.

Written by the indexing model from the issue text.