Use source generator for mapping HTTP API to command handlers

[alexeyzimarev]

Eventuous supports mapping command handlers in command services to HTTP API endpoints. It removes quite a lot of boilerplate code using minimal API feature of latest .NET versions.

However, the feature uses reflections to resolve the service for each API call. Command handler delegates are cached, but it's still not exceptionally fast and also breaks AOT-compatibility because of use of reflections.

It should be relatively straightforward to replace reflections with generated code.

[alexeyzimarev]

Moving it to after 0.15

[linear]

EVE-54 Use source generator for mapping HTTP API to command handlers