sql: support "GLOBAL" privileges

[cockroach-teamcity]

Exalate commented:

Related PR: cockroachdb/cockroach#82166
Commit: cockroachdb/cockroach@430babc

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Release note (sql change): Introduce GLOBAL privileges.
These are privileges that live above the database level.

Example: GRANT SYSTEM MODIFYCLUSTERSETTING TO foo

Currently MODIFYCLUSTERSETTING is the only global privilege,
it allows users to query the crdb_internal.cluster_settings table.

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Note from Rafi: In the docs, we might want to make clear that “global” privileges means “cluster-wide” and has no relation to “global” in the multiregion sense.

Jira Issue: DOC-4597

[exalate-issue-sync]

Rafi Shamim (rafiss) commented:
I’m moving this to the SQL Sessions area where it should belong, and assigning Richard Loveland instead

[exalate-issue-sync]

Richard Loveland (rmloveland) commented:
See also the following docs PR that depends on this work:
#15094
I will be taking over that PR at request of Stephanie Bodoff