Add Basic Replay Integration documentation

[Lms24]

Core or SDK?

Platform/SDK

Which part? Which one?

JS Browser SDKs

Description

As a first step towards having proper documentation for Sentry Replay, we should provide a small code snippet in the "Pluggable Integrations" section of the JS SDK documentation to document how to set up the Replay integration. Surely, to document the entire Replay feature we'll want more documentation but for now, this should do. Also, it adds instructions on how to use Replay as a CDN bundle, which is something, we haven't yet documented properly.

Suggested Solution

Add an entry to "Pluggable Integrations" analogously to how we document other pluggable integrations

[Lms24]

Closing as we now have proper docs for Replay.