Change `start()` API

[billyvg]

Current Status

start() currently creates a new session if it doesn’t exist and does nothing if session was not sampled. Users expect calling this method would override session sampling logic and being recording as if it were sampled for session-based replay.

Proposal

• Does nothing if current session is already sampled for session-based replay
• Starts a session-based replay (session will be sampled)
• Accepts an argument to start a "buffered" replay (i.e. what we do for error-based replays)

[github-actions]

This issue has gone three weeks without activity. In another week, I will close it.

But! If you comment or otherwise update it, I will reset the clock, and if you label it Status: Backlog or Status: In Progress, I will leave it alone ... forever!

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"A weed is but an unloved flower." ― Ella Wheeler Wilcox 🥀