Add feature-flagged Attempts API routes

[Sgtpluck]

Note: this PR is dependent on #11716 which adds the attempts_api_enabled feature flag

🎫 Ticket

Link to the relevant ticket:
Create initial Attempts API endpoints

🛠 Summary of changes

This change adds the three endpoints that will be utilized in the Attempts API.

• A configuration endpoint for discovery (/.well-known/ssf-configuration)
• A status endpoint for API status information (/api/attempts/status)
• A polling endpoint for the eventual data stream (/api/attempts/poll)

Detailed descriptions of the end-state of the endpoints can be found in our technical documentation draft and in the shared signals framework spec.

In this initial change
When the feature flag attempts_api_enabled is set to false:

• All new endpoints 404
  When the feature flag attempts_api_enabled is set to true
• The configuration endpoint returns basic configuration information as detailed here
• The status endpoint returns a 200, with the body disabled and the reason not_yet_implemented
• The polling endpoint returns a 405 method_not_allowed error