[release/8.0-preview1] Split Mono manifest creation into a separate subset

[github-actions]

Backport of #81598 to release/8.0-preview1

/cc @steveisok@directhex

Customer Impact

Enables source build to build workload manifests. Previously, these were only built with the mono runtime, but source build is exclusively coreclr.

Testing

Risk

IMPORTANT: Is this backport for a servicing release? If so and this change touches code that ships in a NuGet package, please make certain that you have added any necessary package authoring and gotten it explicitly reviewed.

[ghost]

I couldn't figure out the best area label to add to this PR. If you have write-permissions please help me learn by adding exactly one area label.

[steveisok]

@carlossanlop this is tell mode. This PR enables source build to build the workload manifests.

[carlossanlop]

Thanks for letting me know. Will merge tomorrow when the branches open after branding.

[ghost]

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Issue Details

---

Backport of #81598 to release/8.0-preview1

/cc @steveisok@directhex

Customer Impact

Enables source build to build workload manifests. Previously, these were only built with the mono runtime, but source build is exclusively coreclr.

Testing

Risk

IMPORTANT: Is this backport for a servicing release? If so and this change touches code that ships in a NuGet package, please make certain that you have added any necessary package authoring and gotten it explicitly reviewed.

Author:	github-actions[bot]
Assignees:	-
Labels:	area-Infrastructure-mono
Milestone:	-

[steveisok]

pinged @mmitche offline and he gave the go ahead.