[RAC] [Uptime UI] Register Uptime UI rule type(s) with new RAC rules registry

[jasonrhodes]

Continuing on from the discussion in #97826, we're going to handle registering rule types separately for each remaining observability app, based on the example work done in APM. This should allow alerts created from these registered rules to begin showing up in the observability alerting table.

AC:

• Uptime rule registry is created as a child of the observability registry (see: APM example)
• Uptime rule type(s) are registered using this new registry (see: APM example)

[elasticmachine]

Pinging @elastic/uptime (Team:uptime)