LP1997098: Add Support for PostgreSQL 15

LP1997098: Add Support for PostgreSQL 15

Add Makefile targets to install the PostgreSQL 15 server
prerequisites.

Make postgresql-client-15 the default client version.

Add full text search configuration for PostgreSQL 15.

Modify config.ccmm_once_per_paramset and config.chmm_once_per_paramset
indexes for the interval casting function change from immutable to
stable.

Add a database upgrade script for the above.

Update the server installation instruction (README) for PostgreSQL 15.

Signed-off-by: Jason Stephenson <jason@sigio.com>
Signed-off-by: Bill Erickson <berickxx@gmail.com>