Null Partition Key for Cosmos

[karunmotorq]

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

[ghost]

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

[karunmotorq]

Solves #19183

[karunmotorq]

@microsoft-github-policy-service agree

[ealsur]

Thanks for your contribution. Can you please clarify the scenario? The description seems to be for Partition Key None but the code is for Null

[karunmotorq]

@ealsur Is there anything else to be done?

[ealsur]

@jhendrixMSFT This PR changes the public API surface adding 1 constructor, should I generate the APIView for approval or can it be spot-reviewed?

[ealsur]

@karunmotorq This PR modifies the public surface, we need approval for public API changes.

[karunmotorq]

@ealsur Is this what was meant?

[ealsur]

There's a typo on the variable name, otherwise looks good :)

[ealsur]

@jhendrixMSFT Are we good on the public surface after the changes?