[FH-2] Open Frames Implementation

[FTCHD]

Description (1,500 PTS)

• This issue is about implementing the OpenFrames standard for all existing and future Frames on FrameTrain.
• It should not require any changes to the BuildFrameData type (ie. the data returned by a handler function). If it does, you must make these changes to all existing templates.
• Implementing this requires touching all parts of the app, especially @/lib/serve.ts and the /f route.
• The preview (/p) route can be kept unchanged, as it's only used in our web editor.
• Ideally the postUrl for OpenFrames should be different than the one for normal Frames. This avoid having too much logic in the /f route. The initial slide of the Frame will always be posted using the /f/${FRAME_ID} route, but the fc:post_url and of:post_url values should be different so that requests are sent to different routes.
• Types should be written directly in the frametrain repository, not by installing a third party package.
• Needs to work with anonymous clients.
• Needs to work with Lens, see this for more info.
• Needs to work with XMTP by checking if the clientProtocol is XMPT and validating the payload using the validateFramesPost function in @xmtp/frames-validator.
• Only a full, thorough, succesful implementation will be accepted.
• You can modify other parts of the app in order to make improvements, however you must make sure it's really an improvement and not a change that just make your task easier (and that's all it does).
• For more information check out the OpenFrames docs.