Fix issue where doublestar globbing only worked at a single level

[djaglowski]

See opentelemetry-collector-contrib#4628

The PR also refactors file finding into a more testable structure, and adds tests.

[codecov]

Codecov Report

Merging #268 (2c3defd) into main (bef2800) will increase coverage by 0.0%.
The diff coverage is 85.7%.

@@          Coverage Diff          @@
##            main    #268   +/-   ##
=====================================
  Coverage   76.4%   76.4%           
=====================================
  Files         94      95    +1     
  Lines       4453    4454    +1     
=====================================
+ Hits        3403    3404    +1     
  Misses       719     719           
  Partials     331     331           

Impacted Files	Coverage Δ
operator/builtin/input/file/finder.go	77.7% <77.7%> (ø)
operator/builtin/input/file/config.go	77.0% <100.0%> (-0.4%)	⬇️
operator/builtin/input/file/file.go	72.3% <100.0%> (+<0.1%)	⬆️

[djaglowski]

The fix boiled down to switching from filepath.Glob to doublestar.Glob, within file_input's poll loop. Because of this, performance is a concern. However, benchmarks appear to show a small improvement:

This branch:

> make bench
go test -benchmem -run=^$ -bench ^* ./...
...
goos: darwin
goarch: amd64
pkg: github.com/open-telemetry/opentelemetry-log-collection/operator/builtin/input/file
cpu: Intel(R) Core(TM) i7-7700HQ CPU @ 2.80GHz
BenchmarkFileInput/Single-8               468024              2194 ns/op             640 B/op          9 allocs/op
BenchmarkFileInput/Glob-8                 118584             10311 ns/op            2570 B/op         36 allocs/op
BenchmarkFileInput/MultiGlob-8            118840             11821 ns/op            2572 B/op         36 allocs/op
BenchmarkFileInput/MaxConcurrent-8         80212             12729 ns/op            2564 B/op         36 allocs/op
BenchmarkFileInput/FngrPrntLarge-8        472976              2140 ns/op             641 B/op          9 allocs/op
BenchmarkFileInput/FngrPrntSmall-8        641103              1933 ns/op             640 B/op          9 allocs/op

main:

> make bench
go test -benchmem -run=^$ -bench ^* ./...
...
goos: darwin
goarch: amd64
pkg: github.com/open-telemetry/opentelemetry-log-collection/operator/builtin/input/file
cpu: Intel(R) Core(TM) i7-7700HQ CPU @ 2.80GHz
BenchmarkFileInput/Single-8               451371              2344 ns/op             640 B/op          9 allocs/op
BenchmarkFileInput/Glob-8                 114730             12301 ns/op            2573 B/op         36 allocs/op
BenchmarkFileInput/MultiGlob-8            115032             12374 ns/op            2573 B/op         36 allocs/op
BenchmarkFileInput/MaxConcurrent-8         80317             12709 ns/op            2563 B/op         36 allocs/op
BenchmarkFileInput/FngrPrntLarge-8        629154              1916 ns/op             641 B/op          9 allocs/op
BenchmarkFileInput/FngrPrntSmall-8        656941              2148 ns/op             640 B/op          9 allocs/op