[WIP] Keep empty lines

[felixfontein]

One annoying thing with SOPS-encrypted files is that all whitespace is normalized, and most importantly empty lines are removed.

I've been thinking for some time whether we can do better, so I did an experiment:

• DotEnv: works fine.
• INI: no way to access empty lines during parsing or emitting. This is due to the INI library used (gopkg.in/ini.v1).
• JSON: no way to access empty lines during parsing or emitting. This is due to the JSON library used (Golang's JSON encoder/decoder).
• YAML: it's possible to emit newlines, but no way to get them during parsing. One can try to use the line numbers from the node objects, but one has no idea how many lines the node itself needed, so no chance....

I guess for JSON it's OK to ignore newlines, but for INI and YAML it would be really nice. Especially for YAML, which I consider the main format for SOPS. Maybe this will be better with https://github.com/goccy/go-yaml...

I'm creating a PR for this experiment so that others can take a look, and maybe it's possible to improve on this once/if we switch to https://github.com/goccy/go-yaml.