feat: install extensions using the catalog

[ericswanson-dfinity]

Description

Look up location of extension.json url from /catalog.json in https://github.com/dfinity/dfx-extensions

Fixes https://dfinity.atlassian.net/browse/SDK-1796

How Has This Been Tested?

Added an e2e test, and the dfx extension install <extension name> test also covers this.

Checklist:

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