AdminSplit and AdminScatter requests are subject to capability checks.
Previously, these capabilities were codified in the "enabled" form. As
such, by default, secondary tenants did not have the ability to perform
these operations. This is in violation of what secondary tenants could
do prior to 23.1, at a time before capabilities existed. Moreover,
RESTORE/IMPORT rely on performing these operations for performance.
This made disallowing these operations by default a performance
regression.

This patch flips the phrasing of how these capabilities are stored on
the proto to use the "disable" verbiage. As such, secondary tenants are
able to perform splits and scatters by default. However, no change is
made to the public interface -- users above the `tenantcapabilitiespb`
package continue to interact with these capabilities as they were
before, oblivious to how these things are stored on disk.

As part of this patch, we also clean up a testing knob that was used by
various backup, CDC, and logictests to override capability checks in the
Authorizer. We no longer need this with the new defaults.

Fixes cockroachdb#96736

Release note: None

Now that tenants are able to perform splits by default, we can cleanup
`TestMultiTenantAdminFunction` to not use a setupCapability concept.

Epic: none

Release note: None

…state

Release note: None