Check minversion of test-proxy prior to push

[scbedd]

• Add a minimum_proxy_version.txt file under eng/ of azure-sdk-assets
• Leverage Merge eng/ from main on assets push #8020 's pull from main ability to check get the updated file from main
• Before a push operation, check running proxy version against this minimum_proxy_version file.
• Error and recommend upgrade if not newer than the target version.
• an eng/common template that can check this same file and error if the running proxy version for CI is below this minimum version.

FYI @gearama this is based on your suggestion in the just-past meeting. This is lower priority than adding a version of credscan or getting that common PR out, but we'll likely get to it pretty quick.