Provide a `buf mod open` equivalent command

[doriable]

Feature

buf mod open was deprecated since buf mod as a whole has been deprecated and there is no current equivalent.
Since this is a fairly simple functionality and is only concerned with remote modules in the BSR, I propose bringing back an equivalent in the buf registry namespace:

buf registry open

This will open all BSR pages to remote modules in the given input, if the input is a workspace with multiple remote modules, it will open all of them. If there are no remote modules in the given input, this is a no-op that exits 0.

[bufdev]

I don't think registry is the right sub-command, but can talk about it.