feat: add support for `dfx canister url <CANISTER>`

[vincent-dfinity]

Description

Add a command for dfx:  dfx canister url <CANISTER> that gives the URL for a canister.

Fixes SDK-1613

How Has This Been Tested?

• tested locally
• e2e tests added at e2e/tests-dfx/canister_url.bash.

Checklist:

• [x] The title of this PR complies with Conventional Commits.
• [x] I have edited the CHANGELOG accordingly.
• [x] I have made corresponding changes to the documentation.