refactor: format source code using nightly rustfmt

[lklimek]

Issue being fixed or feature implemented

We need to unify code formatting.

What was done?

This PR adds .rustfmt.toml file to the repo that defines formatting of Rust code.

1. Created .rustfmt.toml that defines code formatting policy
2. Configured github actions to run using +nightly
3. Run cargo +nightly fmt
4. Updated docs

How Has This Been Tested?

cargo +nightly fmt

Breaking Changes

Will cause tons of conflicts.

Checklist:

• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [ ] I have added or updated relevant unit/integration/functional/e2e tests
• [ ] I have added "!" to the title and described breaking changes in the corresponding section if my code contains any
• [x] I have made corresponding changes to the documentation if needed

For repository code-owners and collaborators only

• [ ] I have assigned this pull request to a milestone