Add MIN/MAX aggregate support for uuid

I noticed that we support various comparison operators on uuid values.
However, we were missing support for the MIN and MAX aggregate
functions, which seems like a logical thing to also support if we
support operators.

The use case that I envision the most is finding the oldest and newest
UUID v7 values in a set. UUID v7 is a timestamp-prefixed identifier.
According to RFC 9562[0], the first 48 bits of a UUID v7 value are
a Unix Epoch timestamp. Additionally, Postgres implements Method 3 of
Section 6.2[1] for UUID v7 such that the next 12 bits bits store a
1/4096 (or 2^12) fraction of sub-millisecond precision. See the comment
in generate_uuidv7() for more details.

[0]: https://datatracker.ietf.org/doc/html/rfc9562#name-uuid-version-7
[1]: https://datatracker.ietf.org/doc/html/rfc9562#monotonicity_counters

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Tristan Partin
PostgreSQL Contributors Team
AWS (https://aws.amazon.com)