Add functional tests for diktat

[aktsay6]

New action made to check if diktat works from cli/from maven/from gradle. Closes #299

Actions checklist

• Implemented Rule, added Warnings
• Added tests on checks
• Added tests on fixers
• Updated diktat-analysis.yml
• Updated available-rules.md

[codecov]

Codecov Report

Merging #312 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #312   +/-   ##
=========================================
  Coverage     82.29%   82.29%           
  Complexity     1016     1016           
=========================================
  Files            52       52           
  Lines          2627     2627           
  Branches        830      830           
=========================================
  Hits           2162     2162           
  Misses          169      169           
  Partials        296      296           

Flag	Coverage Δ	Complexity Δ
#unittests	82.29% <ø> (ø)	1016.00 <ø> (ø)

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[petertrr]

Now you need to make this check green by checking output of all commands and somehow checking if they failed or diktat found errors.

[petertrr]

Also I suggest to move FunctionalTestFile to test resources

[petertrr]

LGTM