[pkg/stanza] Standardize structure of operators

[djaglowski]

Component(s)

pkg/stanza

Describe the issue you're reporting

This is a tracking issue for a set of cleanup operations which would be helpful in the long run. I've noticed while working on #31664 many operators have nonstandard file naming and structure. When attempting to make changes across the codebase, these variations make it more difficult to establish confidence that we're doing things the same in each operator. I'd like to enforce the following patterns in each operator:

1. Operator structs and file names should use the class e.g. Input/input.go, Output/output.go, Parser/parser.go, Transformer/transformer.go.
2. Separate code into config.go and <class>.go.

TODO

• input/file
• input/generate
• input/journald
• input/namedpipe
• input/stdin
• input/syslog
• input/tcp
• input/udp
• input/windows
• output/drop
• output/file
• output/stdout
• parser/csv
• parser/json
• parser/jsonarray
• parser/keyvalue
• parser/regex
• parser/scope
• parser/severity
• parser/syslog
• parser/time
• parser/trace
• parser/uri
• transformer/add
• transformer/assignkeys
• transformer/copy
• transformer/filter
• transformer/flatten
• transformer/move
• transformer/noop
• transformer/recombine
• transformer/remove
• transformer/retain
• transformer/router
• transformer/unquote