Replace strings.SplitN(2) with strings.Cut

[joanlopez]

What?

It updates the calls to strings.SplitN, with n=2 with strings.Cut, because most of the times that's why strings.Cut was added into the Go stdlib, as it makes the code involved more readable.

Why?

I started with a single // TODO I found while working on another task, but then realized that the codebase is plenty of calls to strings.SplitN with n=2, where most all the cases what we really want is to "cut" (split) a string containing key-values (e.g. key:value, key=value, etc).

Checklist

• I have performed a self-review of my code.
• I have added tests for my changes.
• I have run linter locally (make lint) and all checks pass.
• I have run tests locally (make tests) and all tests pass.
• I have commented on my code, particularly in hard-to-understand areas.

Related PR(s)/Issue(s)

[mstoykov]

nice, great job!