[SIEM] Audit our plugin dependencies and their availability

[rylnd]

As part of the New Platform migration, we will necessarily fill out our kibana.json with our required and optional dependencies.

However, I've noticed a few issues in our app that merit the following audit:

1. Verify parity between our plugin dependency types
2. Ensure that those types reflect the availability in kibana.json: e.g. if alerting is optional, we should specify alerting?: AlertingSetup
3. Ensure that our RequestHandlerContext types reflect the availability in kibana.json, as these are independent of either of the above.

Migrating version labels to description:
Affected versions include: v7.8.0, v7.9.0, v8.0.0

[elasticmachine]

Pinging @elastic/siem (Team:SIEM)

[rylnd]

This was closed by #64842; audit report can be found there.