Expose URL discovery behind `--discover`/`discover`

[waldekmastykarz]

Configuring URLs to watch is central to using Dev Proxy. Recently, to simplify discovering URLs to watch, we shipped a discovery preset (#969). Since this preset is unlikely to change, we should simplify using it further, by introducing either an arg (--discover) or a command (devproxy discover) to run Dev Proxy preconfigured in discovery mode. Running discovery this way rather than through a preset would be more visible because it's a part of help and easier to use because it doesn't require providing the path to the discovery preset.

When this is shipped, the discovery preset becomes obsolete and we can remove it.

[garrytrinder]

I agree, let’s not make this more complicated than it needs to be.

I think we should go with ‘--discover’, which would be consistent with ‘--record’ option that we already have for enabling recording mode.

[waldekmastykarz]

I think we should go with ‘--discover’, which would be consistent with ‘--record’ option that we already have for enabling recording mode.

Perhaps we should compliment this with a warning such as Dev Proxy is running in URL discovery mode. Configured plugins and URLs to watch will be ignored.