Adding checks during SAS creation

[souravgupta-msft]

• The purpose of this PR is explained in this or a referenced issue.
• The PR does not update generated files.
  • These files are managed by the codegen framework at Azure/autorest.go.
• Tests are included and/or updated for code changes.
• Updates to CHANGELOG.md are included.
• MIT license headers are included in each file.

[stotz89]

Hi @souravgupta-msft,
This PR has introduced a check within the SignWithSharedKey method:

       if v.ExpiryTime.IsZero() || v.Permissions == "" {
		return QueryParameters{}, errors.New("service SAS is missing at least one of these: ExpiryTime or Permissions")
	}

When the SAS should be associated with stored access policy the documentation says expiry and permissions must be omitted if those information are specified in the associated stored access policy.

Currently this change leads to an error during signing which has worked previously. My code looks like

sasQueryParams, err := sas.BlobSignatureValues{
		Protocol:      sas.ProtocolHTTPS,
		StartTime:     *new(time.Time),
		ExpiryTime:    *new(time.Time),
		Identifier:    policyName,
		ContainerName: containerName,
	}.SignWithSharedKey(credential)

Anything that I have missed that I need to do?
Thanks a lot!