Fix inter issues in master branch

[na--]

What?

We should fix the linter issues that exist in our master branch.

Tasks

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1. k6/html: lint fixes #3701
   +0
2. js/k6/http: Fix lint errors #3566
   maintenance +1
   
3. Fix 51 issues in lib
4. Fix 22 issues in cloudapi
5. Fix 39 issues in metrics
6. Fix rest of the packages
7. Lint fixes #3495
   +0
8. Adressing linter issues in netext, netext/httpext packages #3484
   breaking change maintenance refactor +3
   
9. Fix lint issues in lib/fsext #3482
   maintenance refactor +2
   
10. Linter fixes for the crypto and encoding k6 modules #3460
    lower prio maintenance refactor +3
    
11. Adressing linter issues for the api/v1 package #3463
    lower prio maintenance refactor +3
    
12. Fix lint issues in js/tc39 #3479
    maintenance +1
    
13. Fixes linter issues of the output/influxdb #3481
    maintenance +1
    
14. Minor refactoring of the CSV output #3462
    lower prio maintenance refactor +3
    
15. Fixes linter issues in testutils package #3480
    maintenance +1
    
16. Fix lint issues in api package #3485
    bug maintenance +2
17. Fix lint issues in output/cloud/* #3483
    maintenance +1
    
18. Fix lint issues in js/compiler #3478
    maintenance +1
    

Right now we use the golangci-lint as the main tool for linting. The latest report:

golangci-lint run --out-format=tab | awk 'NF { print $1 }' | sed -E 's|/[^/]*(:[0-9]+){0,2}$||' | uniq -c | sort -rn
 233 js/modules/k6/html
    112 js/modules/k6/http
     48 lib
     38 metrics
     32 lib/executor
     28 lib/netext/httpext
     26 lib/netext
     22 cloudapi
      5 lib/fsext
      5 lib
      3 output/statsd
      3 output/json
      3 js/modules/k6/grpc
      2 lib/types
      2 lib/netext/grpcext
      2 lib/consts
      2 js/modules/k6/metrics
      2 js/common
      2 cmd

Why?

Most of those are about undocumented methods or using underscores or ALL_CAPS in variables, but it's still worth it to spend some time and eliminate, or at least substantially reduce, the number of linter complaints.

Fixing linter issues would significantly help any potential contributors because:

• it forces best practices
• it would force us to improve the in-code documentation, tremendously helping new people who are unfamiliar with the codebase
• it would make the code more idiomatic
• a lot of Go editors have golint/golangci-lint automatically enabled, and when you open some files with them, there are dozens of issues reported
• we can improve our Go report card score, after all we've added it in the top of the README...
• and many more

[na--]

This tool might be helpful for some of the drudge work: https://github.com/cuonglm/gocmt