Async DELETE for APIs resources

[maciejtreder]

ARM (Control Plane) API Specification Update Pull Request

Purpose of this PR

What's the purpose of this PR? Check all that apply. This is mandatory!

• [ ] New API version. (Such PR should have been generated with OpenAPI Hub, per this wiki doc.)
• [ ] Update existing version for a new feature. (This is applicable only when you are revising a private preview API version.)
• [ ] Update existing version to fix swagger quality issues in S360.
• [ ] Other, please clarify:
  • edit this with your clarification

Due diligence checklist

To merge this PR, you must go through the following checklist and confirm you understood and followed the instructions by checking all the boxes:

• [ ] I have reviewed the general guidance on the spec PR review process: https://aka.ms/specprreview.
• [x] I confirm this PR is modifying Azure Resource Manager (ARM) related specifications, and not data-plane related specifications.
• [ ] I commit to follow the Breaking Change Policy.
• [ ] I have reviewed following Resource Provider guidelines, including ARM resource provider contract and REST guidelines (estimated time: 4 hours).
  I understand this is required before I can request review from an ARM API Review board.

ARM API changes review

• If you want for the ARM team to review this PR, you must add the ARMReview label.
• The automation may automatically add the ARMReview label, if appropriate.
  If this happens, proceed according to guidance given in GitHub comments also added by the automation.

Breaking change review

If you have any breaking changes as defined in the Breaking Change Policy, follow the process outlined in the High-level Breaking Change Process doc.

Getting help

• For guidance on fixing this PR CI check failures, see the hyperlinks provided in given failure and https://aka.ms/ci-fix.
• For additional help, see https://aka.ms/azsdk/support/spectools.