iot central minor swagger changes and description fixes

[rafarhat]

Latest improvements:

MSFT employees can try out our new experience at OpenAPI Hub - one location for using our validation tools and finding your workflow.

Contribution checklist:

• I have reviewed the documentation for the workflow.
• Validation tools were run on swagger spec(s) and have all been fixed in this PR.
• The OpenAPI Hub was used for checking validation status and next steps.

ARM API Review Checklist

• Service team MUST add the "WaitForARMFeedback" label if the management plane API changes fall into one of the below categories.
• adding/removing APIs.
• adding/removing properties.
• adding/removing API-version.
• adding a new service in Azure.

Failure to comply may result in delays for manifest application. Note this does not apply to data plane APIs.

• If you are blocked on ARM review and want to get the PR merged urgently, please get the ARM oncall for reviews (RP Manifest Approvers team under Azure Resource Manager service) from IcM and reach out to them.
  Please follow the link to find more details on API review process.

[openapi-sdkautomation]

In Testing, Please Ignore

[Logs] (Generated from 53ee5c8, Iteration 7)

No readme.md specification configuration files were found that are associated with the files modified in this pull request.

[AutorestCI]

Automation for azure-sdk-for-go

Nothing to generate for azure-sdk-for-go

[azuresdkci]

Can one of the admins verify this patch?

[weidongxu-microsoft]

Pending for API board.

@rafarhat Please add code owner of the service to PR (if available) as well. Thanks.

[avneet723]

@yaohaizh This is an update for our Swagger for the same set of IoT Central APIs that we have approval from API review board. Could you please take a look and add the appropriate tag?

[yaohaizh]

@avneet723 @weidongxu-microsoft updated.