feat: Open http and https link in browser

[laomuon]

What does this PR do, and why?

Make the external link in message info pop-up to be opened in the browser when hit Enter

How did you test this?

• Manually - Behavioral changes
• Manually - Visual changes
• Adapting existing automated tests
• Adding automated tests for new behavior (or missing tests)
• Existing automated tests should already cover this (only a refactor of tested code)

Self-review checklist for each commit

• It is a minimal coherent idea
• It has a commit summary following the documented style (title & body)
• It has a commit summary describing the motivation and reasoning for the change
• It individually passes linting and tests
• It contains test additions for any new behavior
• It flows clearly from a previous branch commit, and/or prepares for the next commit

[laomuon]

@zulipbot add "area: UI" "area: event handling" "PR needs review"

[neiljp]

It would be useful to define the protocols we support somewhere as a constant rather than inline here.

[mounilKshah]

Thanks @laomuon for working on this. I tried it and it worked well on my system. In the current state of the PR, I don't have much to add to what Neil has already suggested.