Fix artifact generation to support multi TFM

[kshyju]

Addresses part of #10044

Fix artifact generation to support multi TFM.

Sample run: https://azfunc.visualstudio.com/Azure%20Functions/_build/results?buildId=165387&view=artifacts&pathAsName=false&type=publishedArtifacts

IMPORTANT: Currently, changes must be backported to the in-proc branch to be included in Core Tools and non-Flex deployments.

• Backporting to the in-proc branch is not required
  • Otherwise: Link to backporting PR
• My changes do not require documentation changes
  • Otherwise: Documentation issue linked to PR
• My changes should not be added to the release notes for the next release
  • Otherwise: I've added my notes to release_notes.md
• My changes do not need to be backported to a previous version
  • Otherwise: Backport tracked by issue/PR #issue_or_pr
• My changes do not require diagnostic events changes
  • Otherwise: I have added/updated all related diagnostic events and their documentation (Documentation issue linked to PR)
• I have added all required tests (Unit tests, E2E tests)

[jviau]

I notice we are packing separate nuget artifacts for net6 and net8. This isn't really necessary as a nuget package can contain multiple TFMs with in (and the best match will be referenced during build).

Do we want to ship separate packages, or are we intended to ship 1?

[kshyju]

I notice we are packing separate nuget artifacts for net6 and net8. This isn't really necessary as a nuget package can contain multiple TFMs with in (and the best match will be referenced during build).

Do we want to ship separate packages, or are we intended to ship 1?

Yea, that makes sense. I removed the redundant NuGet packages & also updated the nuget push step.