Update tdigest_aggregate_support output for PG15+

Regress test tdigest_aggregate_support has been failing since at least
Citus 11.0, because of an ommission by citus commit 03832f3 and a change
in the implementation of Postgres random() function (pg commit d4f109e4a)
To reproduce the test diff:
- Checkout tdigest from https://github.com/tvondra/tdigest and `make; make install`
- In citus regress directory run `make check-multi` or `./citus_tests/run_test.py tdigest_aggregate_support`

There are two parts to this commit:

1) Revert "Output: xxxxx" in EXPLAIN VERBOSE output.

Citus commit fe4ac51 normalized EXPLAIN VERBOSE output because of a change
between pg12 and pg13. When pg12 support was no longer required, the rule
was removed from normalize.sed and "Output: xxxx" was reverted in the
impacted regress output files (03832f3), but tdigest_aggregate_support
was ommitted (by 03832f3).

2) Adjust query results; the tdigest_aggregate_support test file has a comment:
 '-- verifying results - should be stable due to seed while inserting the data,
if failure due to data these queries could be removed or check for certain ranges',
but the result values in this commit are consistent across citus 12.0 (pg 15),
citus 12.1 (pg 16) and citus 13.0 (pg 17), or since the Postgres commit that
changed the implementation of random:
https://git.postgresql.org/gitweb/?p=postgresql.git;a=commitdiff;h=d4f109e4a
 so proposing to go with these results.

Note: citus 11.0 (PG14.12) was failing with slightly different query
results, possibly due to floating point difference; added an alternative
regress output file for PG14.