Add sharding_keys to internal_ids

What does this MR do and why?

Adds sharding key to internal_ids table. There are no records (internal link - query plan) on this table where both project_id and namespace_id are NULL. So sharding_key was picked as either one of these.

Note: NOT NULL constraint will be added in #451900

More details can be found here: #435014 (comment 1823507174)

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Related to #435014 (closed)