Tests for operators

[stnokott]

Adds two tests:

• validate that every operator constant in header.go has a role by checking if the Role function is erroneous
• validate that every operator on the official Ubisoft operator page (https://www.ubisoft.com/de-de/game/rainbow-six/siege/game-info/operators) is also present in our header.go

When both of these succeed, we can be pretty certain that our data is complete.
The only uncertainty will be if the IDs in header.go match the replay files.

Closes #31

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@redraskal
Let me know what you think about the added comment in genops.go:

// since we have a test validating that every operator has a role,
// it could be argued that this method does not need to return an error
// and instead could just panic if the role isnt found

[stnokott]

Tests are failing due to #33

[redraskal]

I think panic is ok in that case

[stnokott]

I think panic is ok in that case

I'll change that tomorrow, don't have any more time today.
Or just merge this now and I'll open a new PR for that change, whatever you prefer.

[redraskal]

I think panic is ok in that case

I'll change that tomorrow, don't have any more time today. Or just merge this now and I'll open a new PR for that change, whatever you prefer.

I'll just merge and make a release so everyone has functional Year 8 binaries