Query metrics meta via new tables

[iambriccardo]

New meta tables have been introduced by SNS and in this PR (#69803) functions have been exposed to query such tables.

We would like to query such data in our organization_metrics endpoints.

[iambriccardo]

I would suggest that we create in sentry_metrics/querying/metadata new files like metrics metric_tags and metric_tag_values each of which contains the logic that fetches the data (using the functions defined in #69803).

The reason why I would propose such separation is that we need to port over some business logic from datasource like the get_stored_metrics_of_projects and it will all be in a central place.

[iambriccardo]

We would also like to implement a mechanism for defining which operations are available for which entity, similarly to this:

sentry/src/sentry/snuba/metrics/utils.py

Line 143 in 69d229e

OP_TO_SNUBA_FUNCTION = {

This would bring us into a position where we are fully independent from the old metrics layer code.