fix: handle queries on non-existing table gracefully

[taimoorzaeem]

Add new TableNotFound error and add json error
message for this error. Closes #3697, closes #3602.

[steve-chavez]

Now that we rely on the schema cache for simple table filters, we need to make sure these requests are fast when a schema cache load for relationships is slow (#3046).

There's a test that validates the above behavior (a request with resource embedding is blocked until the schema cache finishes loading):

postgrest/test/io/test_big_schema.py

Lines 10 to 34 in 52591c0

	def test_requests_wait_for_schema_cache_reload(defaultenv):
	"requests that use the schema cache (e.g. resource embedding) wait for the schema cache to reload"
	env = {
	**defaultenv,
	"PGRST_DB_SCHEMAS": "apflora",
	"PGRST_DB_POOL": "2",
	"PGRST_DB_ANON_ROLE": "postgrest_test_anonymous",
	"PGRST_SERVER_TIMING_ENABLED": "true",
	}
	with run(env=env, wait_max_seconds=30) as postgrest:
	# reload the schema cache
	response = postgrest.session.get("/rpc/notify_pgrst")
	assert response.status_code == 204
	postgrest.wait_until_scache_starts_loading()
	response = postgrest.session.get("/tpopmassn?select=*,tpop(*)")
	assert response.status_code == 200
	plan_dur = parse_server_timings_header(response.headers["Server-Timing"])[
	"plan"
	]
	assert plan_dur > 10000.0

We need an additional test that asserts that a table request (with no resource embedding) finishes in a short plan_dur after reloading the schema cache (calling /rpc/notify_pgrst in the test).

[taimoorzaeem]

One last concern, we are still using NotFound error in a couple places, which returns an empty error json:

postgrest/src/PostgREST/ApiRequest/Types.hs

Line 82 in e2dd435

| NotFound

postgrest/src/PostgREST/Error.hs

Line 135 in e2dd435

toJSON NotFound = JSON.object []

This seems fine for now, but maybe should be improved later (add error msg, details etc) for better UX?

[taimoorzaeem]

@steve-chavez Could this get a review? Seems good to me.

[wolfgangwalther]

I tried to backport this, but it doesn't apply cleanly, probably needs some of the refactors before that. So won't backport.

[taimoorzaeem]

I don't think this should be backported anyways as discussed in #3869 (comment).