add branch support for extension installation

[yike5460]

Describe what this pull request is trying to achieve.

We are developing extension to contribute and find the 'Install from URL' tab is not support user to install from specific branch, e.g. dev, prod, we 'd like to add a 'branch name' option to allow user switch from difference branches of the same repo, especially for the extension in development phase with different feature set provided per branch. Existing user experience will remain and new option can be empty.

Additional notes and description of your changes

More technical discussion about your changes go here, plus anything that a maintainer might have to specifically take a look at, or be wary of.

Environment this was tested in

List the environment you have developed / tested this on. As per the contributing page, changes should be able to work on Windows out of the box.

• OS: [Linux, MacOS]
• Browser: [Chrome]
• Graphics card: [TU104GL Tesla T4 64GB]

Screenshots or videos of your changes

If applicable, screenshots or a video showing off your changes. If it edits an existing UI, it should ideally contain a comparison of what used to be there, before your changes were made.

This is required for anything that touches the user interface.

[yike5460]

@AUTOMATIC1111 would you please help to review since we plan to submit an extension allowing user to use cloud resource to accelerate train & inference process. There can be several branches, e.g. we may use 'aigc' as the stable branch for extension and 'dev' as regular development branch.