[v9] Use session storage for sessions

[lforst]

Description

Session updates we send from the Browser SDK should no longer be per pageview. They should have the same lifetime as a Session Replay session.

[lforst]

Strawman proposal: We add a sessioIntegration() with the following options:

interface SessionIntegrationOptions {
  /**
   * The storage type that the SDK uses to store a Session ID that is used for Sessions and Release Health in Sentry.
   * 
   * Possible values:
   * 
   * - `"sessionStorage"` (default) The Session ID is persisted to the browser's `sessionStorage`. Sessions will persist across hard-navigations on the same origin.
   * - `"memory"` The Session ID is stored in memory. Hard-navigations will produce new sessions.
   * 
   * Defaults to `"sessionStorage"`.
   */
  persistence?: 'sessionStorage' | 'memory'
}

The persistence name coincides with a similar/same option and behavior in Posthog. It's just a great name for this option: https://posthog.com/docs/libraries/js#persistence