fixing capitalization on CRI stage and some lints

pkg/logentry/pipeline.go

pkg/logentry/stages/extensions.go

pkg/logentry/stages/extensions_test.go

pkg/logentry/stages/json_test.go

pkg/logentry/stages/regex_test.go

pkg/logentry/stages/util_test.go

pkg/promtail/targets/filetargetmanager.go