meson: Add 'running' test setup, as a replacement for installcheck

To run all tests that support running against existing server:
$ meson test --setup running

To run just the main pg_regress tests against existing server:
$ meson test --setup running regress-running/regress

To ensure the 'running' setup continues to work, test it as part of the
freebsd CI task.

Discussion: https://postgr.es/m/CAH2-Wz=XDQcmLoo7RR_i6FKQdDmcyb9q5gStnfuuQXrOGhB2sQ@mail.gmail.com

src/test/modules/commit_ts/meson.build

@@ -6,6 +6,9 @@ tests += {
     'sql': [
       'commit_timestamp',
     ],
+    # Disabled because these tests require "track_commit_timestamp = on",
+    # which typical runningcheck users do not have (e.g. buildfarm clients).
+    'runningcheck': false,
   },
   'tap': {
     'tests': [