Feature(session replay): add ability to visually reconstruct user sessions

Copied from https://github.com/apache/flagon-useralejs/issues/445

**Problem**

Session replay is a common feature in instrumentation services. As a developer, it's one of the nicest ways to make sense of user behavior and understand the context in which they encountered errors.

UserALE does not support the type of logs needed for this.

**Solution**

Use mutation observer to emit change events, works pretty well
Needs further research (look at [rrweb](https://www.rrweb.io/) as well as [Sentry](https://github.com/getsentry/sentry-javascript/tree/master/packages/replay-internal))
Some problems with size of initial DOM payload

Start with the MutationObserver-based change events described in the issue, then review rrweb and Sentry's replay-internal implementation for relevant approaches. Investigate the initial DOM payload size problem; done means UserALE can emit the required session data and visually reconstruct a user's session.

Written by the indexing model from the issue text.