Update linting to use black formatter

[akchinSTC]

• Reformatted elyra root directory with black formatter

• Added black to lint-server Make target

• Added pyproject.toml (Black only supports use of toml)

• Added black and click to lint requirements, recent release of click 8.1.0 is causing black to fail

• Flake8 conflicts that appear after black reformatting, should we ignore in flake8 or add rules to black to not do this? See https://github.com/elyra-ai/elyra/runs/5776010612?check_suite_focus=true

    W503 - line break before binary operator
    I202 - Additional newline in a group of imports.
    E203 - whitespace before ':'

What changes were proposed in this pull request?

• This PR introduces the use of black to the lint-server target of the Makefile (in conjunction with the existing flake8 pass) in order to produce a consistent code style throughout the python code.

• We've also used this (one-time) opportunity to convert formatted strings (e.g., "{}".format(foo)) to f-strings (e.g., f"{foo}"). This particular "convention" will continue to be enforced via the review process.

How was this pull request tested?

• Existing tests were confirmed to pass.

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