[Core] Use pkginfo to query metadata for Python Package

[haroldrandom]

Description of PR (Mandatory)
The original purpose to pin wheel version is that it requires a big effort to deal with the breaking changes of wheel from 0.30.0 to 0.31.0 and lack of resources back then (#8896).

Now it's time to unpin wheel version as user request, deprecating old way to query metadata of Python Package.
Using pkginfo to query metadata for Python Package to meet Python Core Metadata Specification. ( PEP 241, PEP 314, PEP 345, PEP 566).

azdev and Azure/azure-cli-extensions have already catch up to change:

• azdev extension update-index: using pkginfo to query and dump metadata info.
• update CI check in Azure/azure-cli-extensions. (Unpin wheel version, update CI check azure-cli-extensions#1462)

Related PRs and issues:

• Close {Packaging} upgrade wheel to 0.34.2 #12583
• Close {Docs} Remove stale reference in README to closed issue about extensions #12771
• Fix remove azure-cli-core wheel==0.30 wheel pin #12582
• Fix Make extensions compatible with latest versions of wheel #8923
• Follow up of {Core} hotfix the name of extension of dev type is None if it has incompatibility problem with core #12598

This also fix bug in some scenarios that CLI can not load metadata of dev typle extension, like az extension list -o table in extension interactive.

Testing Guide

Prepare 3 Python version 3.6, 3.7, 3.8 as first.

Wheel type extension

choose some extensions and build them via bdist_wheel or azdev extension build with wheel 0.30.0, 0.31.0, 0.32.0, 0.33.0, 0.34.2, install them by az extension add -s {wheel_filepath}

Dev type extension

choose some extensions and add them directly in development/editable mode via azdev extension add {extension_name} after setup.

then test to show extension/other az commmand udner 3 Python verions respectively.

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[yonzhan]

add to S168

[jiasli]

Please fix typos in the PR title as it directly goes into the release history. Use capitalized "Unpin".

Also, some test commands for Testing Guide section and unit tests will be helpful.

[haroldrandom]

Please fix typos in the PR title as it directly goes into the release history. Use capitalized "Unpin".

Also, some test commands for Testing Guide section and unit tests will be helpful.

added