Add /_mgmt/health endpoint

[vincentsarago]

Right now when we create an application we register a /_mgmt/ping endpoint to enable check for liveliness. This if fine but usually system (e.g Kubernetes) would want to check for readiness (a.k.a make sure database connection works, ...)

stac-fastapi/stac_fastapi/api/stac_fastapi/api/app.py

Lines 364 to 373 in a402be8

	def add_health_check(self) -> None:
	"""Add a health check."""
	mgmt_router = APIRouter(prefix=self.app.state.router_prefix)
	@mgmt_router.get("/_mgmt/ping")
	async def ping():
	"""Liveliness/readiness probe."""
	return {"message": "PONG"}
	self.app.include_router(mgmt_router, tags=["Liveliness/Readiness"])

I propose we register another health endpoint /_mgmt/health which can return more information about the application readiness.

ref: stac-utils/stac-fastapi-pgstac#229

cc @emmanuelmathot