Update that JIT is disabled in all of Aiven's supported PostgreSQL versions

[deanholbrough]

The current documentation states that the JIT is disabled in PostgreSQL 111:

"By default, the JIT feature is disabled in PostgreSQL 11. You can now enable JIT in Aiven for PostgreSQL on a global level or just for a specific database with a simple command that does not require any installation."

This should state it is disabled in all versions of PostgreSQL Aiven supports.

URL of affected page, and any other information

https://developer.aiven.io/docs/products/postgresql/howto/enable-jit.html

Question: Do we list all the versions or just state a generic all version that Aiven supports?