feat: Extension Management

[rbnmk]

Description

Adds functions to

• List all installed AzDo extensions
• Install AzDo extensions
• Remove AzDo extensions
• Basic tests for each of the functions

Related Issue

N/A

Motivation and Context

I need to install extensions during onboarding of new organizations in our solution.

How Has This Been Tested?

Tested it against my own Azure DevOps organization.

Screenshots (if appropriate):

N/A

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[Manbearpiet]

Hi rbnmk, I'll look into your contribution asap.