Added make fmt and make lint rules

[filipecosta90]

This PR is a simple one just to make more verbose the make checkfmt caused errors.
Sample previous output:

checkfmt: Go files must be formatted with go fmt.
Makefile:15: recipe for target 'checkfmt' failed
make: *** [checkfmt] Error 1

Sample new output:

checkfmt: Go files must be formatted with go fmt. Please run `make fmt`
Makefile:15: recipe for target 'checkfmt' failed
make: *** [checkfmt] Error 1

[codecov]

Codecov Report

Merging #38 (77b9c7e) into master (41854dc) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #38   +/-   ##
=======================================
  Coverage   87.50%   87.50%           
=======================================
  Files           2        2           
  Lines         328      328           
=======================================
  Hits          287      287           
  Misses         23       23           
  Partials       18       18           

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[sonarcloud]

Kudos, SonarCloud Quality Gate passed!

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