[Task] add a aad token for getting the acs token in joining a call

[kevinyulu]

Purpose

• Adding a new environment config property aadToken to be used to sent as a header in getting an ACS Token

Does this introduce a breaking change?

[ ] Yes
[x] No

Pull Request Type

What kind of change does this Pull Request introduce?

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[x] Refactoring (no functional changes, no api changes)
[ ] Documentation content changes
[ ] Other... Please describe:

How to Test

• Get the code

git clone [repo-address]
cd [repo-name]
git checkout [branch-name]
npm install

• Test the code

• provide a valid AAD token and ACS Token Url, and Launch the app
• join any call.

What to Check

Verify that the following are valid

• try to see if you can join a call with a valid input above
• try to see if you see an error when joining a call, if you provide an invalid aad token or do not provide aad token

Other Information

[emlynmac]

LGTM