[checker] Checker bin, JSON config file, new Check interface

[kawmarco]

• Added checker command line entry point (checker/main.go) which accepts a JSON configuration file as input (--config-file), containing a list of Checks
• Adapted Check structs to be more friendly to JSON configuration and JSON report output, thinking of the following workflow
  • Developers define CheckFun(CheckArgs) functions, which contain the actual logic of the check, and "register" their functions using registerCheckFun on init() (so that they are registered in a global map and we can then find the check functions by name at runtime)
  • A JSON-friendly Check struct defines how CheckFuns should be called, including CheckArgs, possible remediations and metadata. The config file is a checklist (a list of Check)
  • Calling Check.Run() returns a JSON-friendly CheckResult, containing the result of the Check and the result of the configured remediations

TODO:

• Document pkg/checker/checker.go
• Proper error/exit value on invalid/insufficient arguments (maybe just support one positional argument)?
• Ensure checker binary is in the ramdisk

[insomniacslk]

hey @kawmarco , thanks for the contribution! Could you please re-submit with DCO (just amend the commit with -s), and address the linter warnings?
You may want to run golangci-lint run and fix any other warning before re-submitting (it will be caught by the CI anyway)

[codecov-io]

Codecov Report

Merging #121 into master will decrease coverage by 3.18%.
The diff coverage is 45.45%.

@@            Coverage Diff             @@
##           master     #121      +/-   ##
==========================================
- Coverage   50.17%   46.99%   -3.19%     
==========================================
  Files          14       21       +7     
  Lines         562      798     +236     
==========================================
+ Hits          282      375      +93     
- Misses        252      391     +139     
- Partials       28       32       +4

Impacted Files	Coverage Δ
pkg/checker/commandexecutor.go	10% <10%> (ø)
pkg/checker/interfaces.go	9.41% <12.5%> (ø)
pkg/checker/checkerrepo.go	70.58% <70.58%> (ø)
cmds/checker/main.go	70.96% <70.96%> (ø)
pkg/checker/checker.go	88.88% <88.88%> (ø)
pkg/checker/dmesg.go	0% <0%> (ø)
pkg/checker/colours.go	57.14% <0%> (ø)
... and 2 more

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[insomniacslk]

I've done only a partial review, publishing it to unblock you.

Also note - several files have changed permissions with this commit, they have now an executable bit set where they should not

[tfg13]

Discussed offline, we will reopen this one against uroot after the move is done