Add Linter

[sdiao]

Proposed change(s)

• Add dotnet format linter
• Add pre-commit hook to reformat code automatically
• Format files

Useful links (GitHub issues, JIRA tickets, forum threads, etc.)

Inspired by:
https://github.com/dotnet/format
ML-Agents linter setup: Unity-Technologies/ml-agents#4362

Following the tutorial in https://pre-commit.com/ to set up pre-commit locally.
Run pip install pre-commit-hooks to set up the pre-commit-hooks.
To run a specific hook, you can use pre-commit run mixed-line-ending --all-files
To run the pre-commit check, make some format change locally, e.g. adding trailing whitespace, extra line, extra space. Next run git add <file to be staged>, and git commit -m <msg>, you should see the format will be automatically fixed.

Types of change(s)

• Bug fix
• New feature
• Code refactor - formatting
• Documentation update
• Other (please describe) - add linter to the repo

Testing and Verification

Please describe the tests that you ran to verify your changes. Please also provide instructions, ROS packages, and Unity project files as appropriate so we can reproduce the test environment.

Test Configuration:

• Unity Version: [e.g. Unity 2020.2.0f1]
• Unity machine OS + version: [e.g. Windows 10]
• ROS machine OS + version: [e.g. Ubuntu 18.04, ROS Noetic]
• ROS–Unity communication: [e.g. Docker]

Checklist

• Ensured this PR is up-to-date with the dev branch
• Created this PR to target the dev branch
• Followed the style guidelines as described in the Contribution Guidelines
• Added tests that prove my fix is effective or that my feature works
• Updated the documentation as appropriate

Other comments

[sdiao]

Inspired by ML-Agents repo's config. We are using dotnet format to format C# code.

[sdiao]

Key pre-commit config setup.

[sdiao]

markdown files format are fixed automatically. Instruction to set up: https://pre-commit.com/
To try it out locally, run pre-commit run --files *.md

[sdiao]

Inspired by ML-Agents team's config. We are adding a Github Check here, so that once a pull request is opened, Github will run the pre-commit check as well.

Success check example
Failed check example

[mrpropellers]

use var and a more descriptive name than msg (note: msg abbreviation is ok)

[sdiao]

Would it be good to keep this PR only adding the linter and formatting? Happy to open a separate PR to update the sample code in markdown files.

[sdiao]

Looks we already have a task AIRO-667 to update the doc. Doc changes will be made in a separate PR.

[mrpropellers]

Ok when I expand the code I can see that this "addition" is really just moving it around. Our current rule is that if the code is new, or if you are re-writing older code for some reason, it must be changed to follow the coding standards if it doesn't already. Since this is technically a change and not a move, it's ok to defer.

[peifeng-unity]

LGTM