Grafana Agent - Flow mode support

[jessedrelick]

Is your feature request related to a problem? Please describe.
The Grafana Agent is moving towards Flow mode, away from Static mode. If PromEx supported Flow mode I could future-proof my agent configuration.

Describe the solution you would like to see
A :flow config option could be added to specify that the Flow agent binary should be downloaded instead. Flow mode should also use a different template file for configuration than the existing .yml file.

How would you expect this feature to work
It should work pretty similarly to how PromEx already works, but I am not 100% sure it is not more involved than that. I'd imagine it's a matter of downloading the correct binary, maybe modifying the start command, and use a new template file to configure the agent.

Additional context
I'm mainly interested to know if Flow support is on the roadmap or if it's something that would be harder than I'm thinking to implement. After discussing with the Grafana onboarding team this week it does seem Flow is the future.