golangci-lint: Enable linters

[pjbgf]

Feature Description

We can start with the linters below and expand further as we go:

• [x] errcheck
• [x] govet
• [ ] gosec
• [x] ineffassign
• [x] staticcheck
• [x] unused
• [x] modernize
• [x] dupl
• [x] misspell
• [x] prealloc
• [x] revive
• [x] whitespace
• [x] paralleltest

Such changes tend to stale other active PRs as it will touch a large amount of files, so:

• Let's only start this after #1751 is done.
• Do a single linter per commit - for commit message *: will make the PR validatio check happy.
• A PR may enable multiple linters if the total amount of files changed are up to 15. If more files are affected, please keep a linter per PR.

[ferhatelmas]

@pjbgf you can assign it to me.

[ferhatelmas]

I would suggest gocritic as well. https://github.com/go-critic/go-critic

[onee-only]

How about paralleltest? It could help speed up the tests.