chore: add rust code formatting check

[shikharvashistha]

This commit adds rust code formatting to the CI

closes #1397

[felixfontein]

The test looks good, though I'm not sure whether the placement is good. Right now it is run as part of the functional tests.

I'm wondering whether we should create a new workflow for such linting-style tests. I think it won't hurt to add more static code checks in the future, like staticcheck. What do you think @getsops/maintainers?

[devstein]

@felixfontein I agree that creating a separate workflow for linting would be preferable. I don't have a strong opinion whether it's done in this PR or a future one.

@shikharvashistha thanks for contributing!