refactor(restore/backup): structure pgBackRest options as map for safer and flexible

[tsivaprasad]

This PR refactors the restore and backup logic to support structured pgBackRest options via maps instead of raw string arrays.

Validation:

1. Set up a 3-node cluster environment.
2. Created a database, added a table, and inserted some rows.
3. Took a backup of the database.
4. Created a new database based on the one from step 2, and added a few more rows to it.
5. Performed an in-place restore using the following configuration:

{
   "restore_config": {
        "provider": "pgbackrest",
        "source_database_id": "f2f1cae9-6f37-4609-aa98-d0991bff3493",
        "source_node_name": "n1",
        "source_database_name": "my_app",
        "repository": {
            "id": "e45dfd13-b318-4ce2-acbe-dd07a7c1c006",
            "type": "posix",
            "base_path": "/backups/container"
        },
         "restore_options": {
            "set": "20250612-083439F"
        }
    }
}

6. Confirmed that the restore worked correctly and brought back the original data from step 2.
7. Added unit tests to verify that basic options, keys with & without '--' prefix, and values containing whitespace are correctly converted from a map to an array.

PLAT-100