[FEATURE] Offline mode

[rgmvisser]

Is your feature request related to a problem? Please describe.
Offline development

Describe the solution you'd like
Add an "offline" flag where the CLI doesn't try to fetch the current secrets (every request tries 5 times by default with 10s timeout), but just immediately uses the locally stored secrets. Other solution could be detection that the computer is offline and don't attempt to fetch them automatically.

Describe alternatives you've considered
Setting --timeout and --attempts to low amounts, but this is a bit cumbersome

Additional context
When developing on planes without wifi etc. this would be nice.

[Piccirello]

The --fallback-only flag will accomplish this when using doppler run. It might be nice to have an --offline alias for this.

[rgmvisser]

That's what I was looking for, thanks!