Insertion pipeline should flag attempt to insert packages with same version

[JanKrivanek]

Context

If we do not bump MSBuild version between insertions, the second push to internal nuget feed cannot succeed (it's not allowed to overwrtie packages) and hence the VS built would be consuming the previous version.

Example

First run - https://devdiv.visualstudio.com/DevDiv/_build/results?buildId=10702496&view=logs&j=44efdce4-6327-5b59-a62d-5dea5650e609&t=4d68204a-0233-5f66-4f6e-6a0bb2607a94&l=38:

Trying to authenticate with auth token.
Successfully authenticated.
Adding package Microsoft.Build.Framework.17.13.0.nupkg to feed VS on [https://devdiv.pkgs.visualstudio.com/.](https://devdiv.pkgs.visualstudio.com/)
Trying to add package to feed without uploading.
Adding package to feed.
The package content is not already on the service.
Uploading package content.
Done uploading package content.
Adding package to feed.
Successfully added package to feed.

Second run - https://devdiv.visualstudio.com/DevDiv/_build/results?buildId=10705646&view=logs&j=44efdce4-6327-5b59-a62d-5dea5650e609&t=4d68204a-0233-5f66-4f6e-6a0bb2607a94&l=40:

The feed already contains 'Microsoft.Build.Framework 17.13.0'.
Trying to authenticate with auth token.
Successfully authenticated.
Adding package Microsoft.Build.Framework.17.13.0.nupkg to feed VS on [https://devdiv.pkgs.visualstudio.com/.](https://devdiv.pkgs.visualstudio.com/)
Trying to add package to feed without uploading.
Adding package to feed.
The package content is not already on the service.
Uploading package content.
Done uploading package content.
Adding package to feed.
POST (https://devdiv.pkgs.visualstudio.com/_apis/packaging/97a41293-2972-4f48-8c0e-05493ae82010/nuget/packages) failed. ActivityId: edb8d61c-064a-4725-8208-19a1393690b4, HTTP Status: Conflict, AFD Ref: Ref A: 81121425BAB84974AEAD6EC04800A5F4 Ref B: CO1EDGE1506 Ref C: 2024-12-13T07:33:23Z

Pushing to the feed in the second run failed - but the overall run succeeded and VS insertion was created.

[JanKrivanek]

Btw. there are cases where it's helpful to be able to rerun the insertion while ignoring the package upload errors (or completely skip the step) - e.g. in case of intermittent git errors during the insertion PR creation. It'd be good not to be forced to create another commit in such case.
So possibly we might want to configure execution of that step with another pipeline variable?