[FEATURE REQ] Document https://management.azure.com/batch

### API Spec link

None yet

### API Spec version

2020-06-01

### Please describe the feature.

I could not find where the batch endpoint is documented in the rest api specs, so please document it. It's being used extensively by portal, ansible, etc but I could not locate official docs by msft on it.

curl 'https://management.azure.com/batch?api-version=2020-06-01' \
-H 'accept: */*' \
-H 'accept-language: en' \
-H 'authorization: Bearer .... \
-H 'content-type: application/json' \
--data-raw $'{"requests":[{...}]'

I've seen discussion in sdks about using it, but sofar they do not do it because it's not available in the rest api specs:
https://github.com/Azure/azure-sdk-for-go/issues/23799
https://github.com/Azure/azure-sdk-for-go/issues/17155
https://github.com/Azure/azure-sdk-for-go/issues/15957
https://github.com/Azure/azure-sdk-for-python/issues/9271
https://github.com/Azure/autorest.typescript/issues/34

No implementation file or test is named. Start by reviewing the repository's REST API specification conventions and the linked SDK discussions, then determine how the Azure management batch endpoint and version 2020-06-01 should be represented; done means the endpoint is documented in the REST API specs and validation passes.

Written by the indexing model from the issue text.