Fix DateTime issue restoring deleted webapp

[mbentancour]

Fixes issue that prevents restoring deleted WebApps if the host running the script uses a locale with a different date format than en-US.

Description

Set en-US as locale when parsing the DeletedTimeStamp.

Checklist

• I have read the Submitting Changes section of CONTRIBUTING.md
• The title of the PR is clear and informative
• The appropriate ChangeLog.md file(s) has been updated:
  • For any service, the ChangeLog.md file can be found at src/{{SERVICE}}/{{SERVICE}}/ChangeLog.md
  • A snippet outlining the change(s) made in the PR should be written under the ## Upcoming Release header -- no new version header should be added
• The PR does not introduce breaking changes
• If applicable, the changes made in the PR have proper test coverage
• For public API changes to cmdlets:
  • a cmdlet design review was approved for the changes in this repository (Microsoft internal only)
    • {Please put the link here}
  • the markdown help files have been regenerated using the commands listed here

[ghost]

Thank you for your contribution mbentancour! We will review the pull request and get back to you soon.

[ghost]

All CLA requirements met.

[isra-fel]

Thanks for the contribution! 😁
@Kotasudhakarreddy Hi Kota, would you mind to review this PR?

[mbentancour]

@isra-fel @Kotasudhakarreddy Let me know if you need any information or clarification from my side.

[isra-fel]

Since we couldn't get a review from service team and yet the code looks good to me. I'll go ahead a merge it.