[Azure] Allow resource group specifiation for Azure instance provisioning

[landscapepainter]

This resolves #3659

Tested (run the relevant ones):

• Code formatting: bash format.sh
• Any manual or new tests for this PR (please specify below)
  • Restart a stopped instance created with resource group specified.
  • Relaunch on existing running cluster that was created with resource group specified.
  • launch with storage_account along with resource_group_vm both specified at ~/.sky/config.yaml
  • Test Instance Deletion After Resource Group Switch
  1. create an instance, A, specifying one RG
  2. change the specified RG to another RG
  3. create another instance, B, with switched RG
  4. keep the RG used for B at config.yaml and remove A
  5. Check if A is removed successfully.
  • Check if replicas with sky serve up is created at the specified resource group.
• All smoke tests: pytest tests/test_smoke.py
  • pytest tests/test_smoke.py --azure except:
  1. tests/test_smoke.py::test_cancel_pytorch
• Relevant individual smoke tests: pytest tests/test_smoke.py::test_fill_in_the_name
• Manual backward compatibility tests:
  • Ensure proper handling of Azure instances across different branches with and without resource group specification
  1. Create an Azure instance from master branch using default resource group name
  2. switch to resource group specification branch
  3. create an instance with resource_group_vm specified
  4. delete the instance created from master branch
     • check if it removes the entire RG
  5. delete the instance created from RG specification.
     • check if it removes the VM, attached resources, deployments, and role assignment without removing resource group.

[romilbhardwaj]

@landscapepainter if we plan to get this in for 0.7, can we resolve merge conflicts so we can start reviewing?