Add --version to cli

[BraisGabin]

Closes #2382

This PR adds the --version flag. It prints the version of the running detekt cli.

I have a problem testing this. And It's that whichVersion() retutns null in test mode. Any idea?

[schalkms]

You were just a few seconds faster than me in regards to the PR for this topic. 😉
I guess it is because of the manifest file that couldn't be loaded.

[arturbosch]

I think it is because of these lines:
https://github.com/arturbosch/detekt/blob/25a8555c03e680096dcf390f23b4a51eea78aaee/detekt-cli/build.gradle.kts#L18-L23
The manifest file is only available inside the jar.
Will it help if you hardcode a manifest file inside the test/resources?

[BraisGabin]

Yes! adding a manifest in the test resources did the trick.

I edited the code too. I we can't know the version of detekt we should fail the task. We don't want to exit with a success because that can mess up the scripts of the users.

I can't test the failure case but it should never happen.

[codecov-io]

Codecov Report

Merging #2383 into master will increase coverage by 0.08%.
The diff coverage is 71.42%.

@@             Coverage Diff              @@
##             master    #2383      +/-   ##
============================================
+ Coverage     82.73%   82.81%   +0.08%     
- Complexity     2135     2141       +6     
============================================
  Files           352      353       +1     
  Lines          6080     6087       +7     
  Branches       1109     1111       +2     
============================================
+ Hits           5030     5041      +11     
+ Misses          480      476       -4     
  Partials        570      570

Impacted Files	Coverage Δ	Complexity Δ
...ain/kotlin/io/gitlab/arturbosch/detekt/cli/Main.kt	38.46% <100%> (+2.46%)	7 <0> (+1)	⬆️
.../kotlin/io/gitlab/arturbosch/detekt/cli/CliArgs.kt	100% <100%> (ø)	7 <0> (ø)	⬇️
...ab/arturbosch/detekt/cli/runners/VersionPrinter.kt	60% <60%> (ø)	2 <2> (?)
...lin/io/gitlab/arturbosch/detekt/core/DebugUtils.kt	58.33% <0%> (ø)	0% <0%> (ø)	⬇️
.../arturbosch/detekt/cli/runners/SingleRuleRunner.kt	97.22% <0%> (+8.33%)	8% <0%> (+2%)	⬆️
...ab/arturbosch/detekt/cli/runners/ConfigExporter.kt	80% <0%> (+60%)	2% <0%> (+1%)	⬆️

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