LB-1532: Add API endpoints for user data export

[pranavsource1]

Problem

Users need a way to export their ListenBrainz data (listens, feedback, etc.) programmatically or via the web interface. Currently, there is no dedicated API to trigger and retrieve these exports asynchronously.

Solution

Implemented a new User Data Export API to handle asynchronous data exports.

• New API Endpoints (/1/export/):

  • POST /: Triggers a new export task.
  • GET /: Lists historical exports for the authenticated user.
  • GET /<export_id>: Retrieves status and details of a specific export.
  • GET /<export_id>/download: Redirects to the download URL for the exported file.

• Backend Changes:

  • Added listenbrainz/webserver/views/export_api.py containing the ExportAPI view class.
  • Registered the new blueprint in listenbrainz/webserver/__init__.py.

• Testing:

  • Added listenbrainz/webserver/views/test/test_export_api.py.
  • Verified functionality with integration tests covering creation, listing, retrieval, and authorization.

• I have run the code and manually tested the changes

AI usage

• I did not use any AI
• I have used AI in this PR

If you did use AI:

• I used AI tools for communication
• I used AI tools for coding
• I understand all the changes made in this PR

Action

None