Add a new function GetOldVesion to VersionBumper to avoid duplicated version

[chenlei-yang]

Description

Add a new function GetOldVersion to VersionBumper and move the former logic into this new function. After getting the old version from the built module manifest, add two checkers to get versions from PSGallery and TestGallery to make sure the old version is the maximum version. So that it can ensure the generated version will not conflict with the preview version on PSGallery or TestGallery.

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)
  • the markdown help files have been regenerated using the commands listed here