Add a Post-Disconnect Shell Script option to run a script when the database connection is terminated

## Enhancement request
It would be nice to have a Post-Disconnect (or Shutdown) Shell Script option like the Pre-Connect Shell Script that runs when the connection to the database is terminated.

My use case it that I use the Pre-Connect Shell Script to start up Google's `cloud_sql_proxy` in the background and there is no convenient way to stop the process when I disconnect from the database. The proxy is left running until I manually kill it from the command line.

I do something like this in the Pre-Connect
```
GOOGLE_APPLICATION_CREDENTIALS="$HOME/.credentials/.json"
export GOOGLE_APPLICATION_CREDENTIALS
/cloud_sql_proxy -instances=::=tcp:5432 &
```

and want to do something like this in the Post-Disconnect

```pkill cloud_sql_proxy```

## What software versions are you using?

Postico version:
2.1.1 (9692)

macOS version:
Sonoma 14.6.1 (23G93)

PostgreSQL version:
PostgreSQL 9.6.24 on x86_64-pc-linux-gnu, compiled by Debian clang version 12.0.1, 64-bit

No files or tests are named. Start by locating the existing Pre-Connect Shell Script option and tracing the database disconnect lifecycle; add the corresponding Post-Disconnect or Shutdown option and verify that its configured script runs when the connection terminates, including the cloud_sql_proxy cleanup use case.

Written by the indexing model from the issue text.