Implement an advisory lock to ensure only one application is running with a given configuration

After the configuration is validated but before we set up the publication start a new thread / channel. This thread should be alive while the application is running.

1. Open a connection to the PostgreSQL database server.
2. Start an advisory lock.
3. Ensure that the connection is kept open by periodically sending SELECT 1;
4. If the connection is broken, retry the connection.

Getting an advisory lock:

SET lock_timeout='100ms';
SELECT pg_advisory_lock(123) -- this value will be configurable in the config.yml file

-- Loop here in go and invoke `SELECT 1`

• If the lock acquisition fails (canceling statement due to lock timeout) stop the application.
• If the SELECT 1 query fails (connection issue), stop the application.
• Add a log entry before invoking the queries (debug level): "Requesting advisory lock (value)"
• Add a log entry after the advisory lock is successfully taken (debug level): "Advisory lock taken (value)"
• For now, hardcode the advisory lock value (123) in a variable. This will be configurable.

Note: At a later point we'll implement a retry mechanism so we don't have to stop the application immediately.