Sarif merging

**Is your feature request related to a problem? Please describe.**

GitHub Actions no longer accepts multiple sarif files for upload.
This is biting my in every project where I use analyzers.

**Describe the solution you'd like**
Can we add a MSBuild target that accepts an array/list of projects and invokes the cli in one go?

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**Describe alternatives you've considered**
It is possible to merge these sarif files, see https://github.com/fsprojects/fantomas/blob/1a6f2dbff5bf25b4fd9fbd6315a8b8cf8bb005f8/sarif.fsx#L231

But that requires everyone to deal with this themselves.
So maybe a breaking change in the MSBuild targets is the simpler thing.

**Additional context**
I don't have the right answer here, happy to discuss.