perf: avoid allocations with (*regexp.Regexp).MatchString

[Juneezee]

We should use (*regexp.Regexp).MatchString instead of (*regexp.Regexp).Match([]byte(...)) when matching string to avoid unnecessary []byte conversions and reduce allocations.

Example benchmark:

var allowedOrigin = regexp.MustCompile(".*.example.com")

func BenchmarkMatch(b *testing.B) {
	for i := 0; i < b.N; i++ {
		if match := allowedOrigin.Match([]byte("www.example.com")); !match {
			b.Fail()
		}
	}
}

func BenchmarkMatchString(b *testing.B) {
	for i := 0; i < b.N; i++ {
		if match := allowedOrigin.MatchString("wwww.example.com"); !match {
			b.Fail()
		}
	}
}

Result:

goos: linux
goarch: amd64
pkg: github.com/gotify/server/v2/api/stream
cpu: AMD Ryzen 7 PRO 4750U with Radeon Graphics
BenchmarkMatch-16          	 2076819	       647.7 ns/op	      16 B/op	       1 allocs/op
BenchmarkMatchString-16    	 2536326	       442.0 ns/op	       0 B/op	       0 allocs/op
PASS
ok  	github.com/gotify/server/v2/api/stream	3.552s

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (92916f0) 86.14% compared to head (ec3e140) 86.14%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #604   +/-   ##
=======================================
  Coverage   86.14%   86.14%           
=======================================
  Files          45       45           
  Lines        1609     1609           
=======================================
  Hits         1386     1386           
  Misses        138      138           
  Partials       85       85           

Files	Coverage Δ
api/stream/stream.go	100.00% <100.00%> (ø)
auth/cors.go	100.00% <100.00%> (ø)

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[jmattheis]

Thanks for your contribution. I don't think the performance is really a problem here, but given that we have a string MatchString fits better to this use-case.