[FEATURE] Allow activating saved connection, similar to `nmcli connection up`

[joshwd36]

Is your feature request related to a problem? Please describe.
The current connect function creates a new connection if a saved one doesn't exist. It also has possible behaviour such as deleting a connection and rebuilding it if the connection attempt failed. I would like to be able to simply try to activate a saved connection, referring to it either by UUID or by connection name, and have an error returned if this failed.

Describe the solution you'd like
A method on NetworkManager with signature similar to:

async fn activate_connection(&self, uuid: &str) -> Result<()>;

For Developers- what would your solution be?
I'm not too familiar with the codebase, but I see that connect calls an activate_connection function, so wrapping this may be a viable approach

Additional context
Add any other context or screenshots about the feature request here.