Merge backup data support

[8ugMak1r]

Suppose I have backup below:

=====================================================================
 StartTime           EndTime              Mode    Size   TLI  Status
=====================================================================
2022-09-26 22:08:10  2022-09-26 22:10:13  INCR   15MB      1  OK
2022-09-26 20:08:10  2022-09-26 20:10:13  INCR   15MB      1  OK
2022-09-26 17:08:10  2022-09-26 17:10:13  FULL   102MB     1  OK

And I want to merge all of it by excuting pg_rman merge xxx, and the backup will be like:

=====================================================================
 StartTime           EndTime              Mode    Size   TLI  Status
=====================================================================
2022-09-26 22:08:10  2022-09-26 22:10:13  FULL   122MB     1  OK

Why I need this feature:

1. make recover fast
2. reduce backup size (removing old data file and arch log)
3. frequently full backup big size database is a bad idea (for reason1)