benchmark recurseKustomizationFiles()

[darkowlzz]

Add benchmark for recurseKustomizationFiles() to measure the performance
of recursively loading kustomization files with certain percentage of
symlinks in the kustomizations.
Follow up of #619 .

Benchmark results for 10/100/1000/10000 kustomization nodes and 10/80 % of them
as symlinks:

goos: linux
goarch: amd64
pkg: github.com/fluxcd/kustomize-controller/controllers
cpu: 11th Gen Intel(R) Core(TM) i7-11850H @ 2.50GHz
BenchmarkRecKust10Nodes10pcSymlink
BenchmarkRecKust10Nodes10pcSymlink-16               3612            338960 ns/op
BenchmarkRecKust10Nodes80pcSymlink
BenchmarkRecKust10Nodes80pcSymlink-16               3486            352937 ns/op
BenchmarkRecKust100Nodes10pcSymlink
BenchmarkRecKust100Nodes10pcSymlink-16               362           3525207 ns/op
BenchmarkRecKust100Nodes80pcSymlink
BenchmarkRecKust100Nodes80pcSymlink-16               334           3516026 ns/op
BenchmarkRecKust1000Nodes10pcSymlink
BenchmarkRecKust1000Nodes10pcSymlink-16               36          34954831 ns/op
BenchmarkRecKust1000Nodes80pcSymlink
BenchmarkRecKust1000Nodes80pcSymlink-16               30          37354662 ns/op
BenchmarkRecKust10000Nodes10pcSymlink
BenchmarkRecKust10000Nodes10pcSymlink-16               3         382599694 ns/op
BenchmarkRecKust10000Nodes80pcSymlink
BenchmarkRecKust10000Nodes80pcSymlink-16               3         382828839 ns/op

[pjbgf]

Do we want to also report on allocs so we can grasp the impact as the code changes?

Suggested change

	b.StartTimer()
	b.StartTimer()
	b.ReportAllocs()

[pjbgf]

great initiative @darkowlzz, looking forward to some benchmarks across the project. 🚀 🎉