filters/builtin: minor performance optimization for sanitize in StripQuery Filter

[trkohler]

This is continuation of https://github.com/zalando/skipper/pull/2918/files

I have discovered that for certain cases string builder performs better than buffer, which is usually a go-to option for Go Developers. String builder was introduced in 1.10+ Go.

results (also attached to last commit message)

pkg: github.com/zalando/skipper/filters/builtin
           │   HEAD~1    │                HEAD                │
           │   sec/op    │   sec/op     vs base               │
Sanitize-8   802.1n ± 0%   748.3n ± 0%  -6.71% (p=0.000 n=10)

           │   HEAD~1   │                HEAD                │
           │    B/op    │    B/op     vs base                │
Sanitize-8   472.0 ± 0%   192.0 ± 0%  -59.32% (p=0.000 n=10)

           │   HEAD~1   │               HEAD                │
           │ allocs/op  │ allocs/op   vs base               │
Sanitize-8   15.00 ± 0%   14.00 ± 0%  -6.67% (p=0.000 n=10)

[AlexanderYastrebov]

Please include benchstat results (without 10+10 before/after benchmark outputs) into last commit message (and update PR description).

I'd also suggest to prefix commit messages with a package name, e.g.:
filters/builtin: introduce benchmark for stripQuery filter

[trkohler]

I attached benchmark results in last commit (afdd426)

I have also tried to use AppendQuoteToASCII, but it resulted in some failed tests. And when I do atempts to fix it properly, there are more allocations happening and it degrades benchmark result. Probably, I use it incorrectly... For now, I let the line be unchanged.

I've also re-wrote description pointing out my motivation for a contribution. I'm sorry if previously it was thought as some issue with time-pressure. It is not pressuring at all, it's just my attempt to do an enhancement on some small part of source code. I thought that if it would succeed, I can try something bigger next.

[AlexanderYastrebov]

You'd need to git commit --amend -s to add DCO to the last commit.
Please include benchstat results (without individual benchmark outputs) to the last commit and PR description to demonstrate the improvement .

[AlexanderYastrebov]

Please use err instead of e like elsewhere.

[AlexanderYastrebov]

👍

[trkohler]

👍