Remove dependency on azure.json

[feiyushi]

As discussed in #204, aad-pod-identity is to use its own configuration to run mic. In this implementation, it uses a k8s secret to store the information that mic needs traditionally from the azure.json.

[kkmsft]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[kkmsft]

Thank you @feiyushi for this contribution. In general /lgtm from my side.

A few notes:

• The understanding is that the docs for usage will come in as another PR.
• For e2e, we will have to have another setting (via an env variable or so) to use the new deployment model and also have the setup steps in setup.sh(in the e2e directory) for setting up the secrets corresponding to this.

[kkmsft]

/cc @khenidak for a look since overall azure.json is tracked #204

[kkmsft]

Thank you, @feiyushi. Merging this PR. We can do the doc and E2E test in the next PR.