add prefect dashboard open to open dashboard from CLI

[zzstoatzz]

follow up to #11519

this PR moves prefect cloud open to prefect dashboard open so that it can also coherently support opening the oss dashboard

[codspeed-hq]

CodSpeed Performance Report

Merging #14985 will not alter performance

_{Comparing prefect-server-open (1a73ede) with main (d867dd0)}

Summary

✅ 4 untouched benchmarks

[desertaxle]

Could prefect cloud open and prefect server open be consolidated under prefect dashboard open?

[zzstoatzz]

Could prefect cloud open and prefect server open be consolidated under prefect dashboard open?

yeah it could if you think that'd be better, i just figured i'd keep the current subgroups and pattern. i don't feel strongly

[desertaxle]

Yeah, I think it'd be a better UX if there were only one command. Then, the user doesn't need to change which command to run based on their current profile.