Blocking the use of different versions of Postgres

#### Issue
Currently, you can use different versions of Postgres when you connect a storage with a different version of Postgresql, which can lead to incorrect operation.

It is necessary to implement a restriction on the use of different versions of postgres with the introduction of a new version of [charmed-postgresql-snap](https://github.com/canonical/charmed-postgresql-snap)

#### Implementation
Blocking the use of different versions of Postgres

#### Test cases
Check the use of different versions postgresql.

The issue names no source files, tests, or entry points. Start by locating the storage connection and PostgreSQL version handling, then inspect how the charm detects the versions of the existing storage and the new charmed-postgresql-snap. Done means mismatched PostgreSQL versions are rejected and the described version-mismatch test cases pass.

Written by the indexing model from the issue text.