Factor pluggable modules out of `runtime/service`

This is a proposal to refactor inter-module dependencies in order to allow easier selection of pluggable features in downstream builds.

* Move pluggable (optional) module dependencies out of `runtime/services` into `runtime/server`
* Move the majority of integration tests into new sub-modules under the pluggable components
- Example: `persistence/relational-jdbc/tests`
- Prior art: `extensions/auth/opa/tests`
* Run "smoke tests" for the default set of plugins under the `runtime/server` module (e.g. validating PostgreSQL integration, but without extensive code coverage, which will be done under `persistence/relational-jdbc/tests`).

The functionality provided by the `runtime/server` module will not be altered by this change.

Pros:
* It will be easier to select a sub-set of optional features to include in downstream builds (some of which may not need all of the pluggable features)
* The `runtime/service` module becomes lean and focused on Polaris fundamentals.

Cons:
* CI time may increase due to having to perform more Quarkus builds for integration tests (might be mitigated by parallel execution).

Start by reviewing the runtime/service and runtime/server module boundaries, then compare the proposed persistence/relational-jdbc/tests layout with extensions/auth/opa/tests. Map optional dependencies and integration tests before deciding how to split them. Done means pluggable dependencies are separated, coverage moves under component tests, and runtime/server retains smoke tests for the default plugins without changing its functionality.

Written by the indexing model from the issue text.