feat: adding read only mode

[jay-babu]

tested with postgres. does something similar to datagrip and lazysql
where the enforcement is based on parsing the input and not a parameter
in a connection

[reegnz]

For postgresql it makes more sense to control this in the connection URL itself:
https://kmoppel.github.io/2025-03-27-til-starting-in-read-only-the-easy-way/
https://www.postgresql.org/docs/current/runtime-config-client.html#GUC-DEFAULT-TRANSACTION-READ-ONLY

So specifically for postgres if you want to make 'read_only' a 1st-class dbui feature, it should set that connection flag in the connection url for psql instead of a messy query parsing. But I think this should be fully handled at the connection URL level and vim-dadbod-ui should stay oblivious to it. Keep it simple.

Example connection URL:

postgresql:///postgres:postgres@127.0.0.1:5432/postgres?options=-cdefault_transaction_read_only%3Don

With this you get messages like:

ERROR:  cannot execute CREATE TABLE in a read-only transaction