sql: Add telemetry for materialized views

[vy-ton]

We are missing 20.2 telemetry for materialized views.

[blathers-crl]

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[vy-ton]

@solongordon Can we make sure this gets prioritized for Milestone D?

[rafiss]

@RichardJCai will take over this issue.

@otan may have seen telemetry for this. Need more information on which specific things need to be tracked. (What name should it reported under? When should the feature counter be incremented?)

[vy-ton]

Feature counters can be incremented for the following commands. The existing counters for views are prefixed with sql.schema.create_view so we can use sql.schema.x_materialized_view

CREATE MATERIALIZED VIEW
REFRESH MATERIALIZED VIEW
ALTER MATERIALIZED VIEW
DROP MATERIALIZED VIEW