Enable golangci linters

[janisz]

Enable following checks in .golangci.yml.
Every PR should fix one rule. There is a chance that some rules are already fixed and we only need to enable them.
After including new rule, please ensure make golangci-lint is passing if there are errors please fix them.
In case there are too many errors feel free to make smaller PRs and enable rules only for specific subdirs (example) or excluding tests (example).

• dogsled
• dupl
• funlen
• gocognit
• goconst
• gocyclo
• godot
• gomnd
• goprintffuncname
• lll
• misspell
• nakedret
• nestif
• prealloc
• unconvert
• unparam
• unused
• usestdlibvars
• whitespace
• wsl

[pawiecz]

Is there a priority or a preferred order for enabling linters listed above? Or should these just be enabled one by one in given order?

[janisz]

@pawiecz There is no priority. You can choose whatever you want. What's more some of the checks might be better to split into multiple PRs and enable directory by directory.