Add Code of Conduct

[omalyshe]

Description

We are adopting Contributor Covenant Code of conduct to let the community know what is expected from them and to maintain a healthy environment for contributors.

Fixes # - issue number(s) if exists

• [x] - git commit message contains an appropriate signed-off-by string (see CONTRIBUTING.md for details)

Type of change

Choose one or multiple, leave empty if none of the other choices apply

Add a respective label(s) to PR if you have permissions

• [ ] bug fix - change that fixes an issue
• [ ] new feature - change that adds functionality
• [ ] tests - change in tests
• [ ] infrastructure - change in infrastructure and CI
• [x] documentation - documentation update

Tests

• [ ] added - required for new features and some bug fixes
• [x] not needed

Documentation

• [ ] updated in # - add PR number
• [ ] needs to be updated
• [x] not needed

Breaks backward compatibility

• [ ] Yes
• [x] No
• [ ] Unknown

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Other information