Add with-nlg option for serializing NLG output

[inariksit]

I got the impression that this was needed for @Meowyam to get the NL output to display in the other window.

Two things:

1. By default: NL output is printed in generated/nlg_en/output.txt
2. With --nlg-only: only NL output is printed to stdout.

Example run:

$ cabal run lam4-cli -- --nlg-only examples/lottery.l4
A Lottery is Info about a lottery. . Each Lottery has associated with it information like 
   * its total_jackpot ; i.e. how much can be won from the jackpot. 
   * its tax deductible status ; i.e. whether buying tickets from this lottery is tax deductible.

[ym-han]

I have revised the CLI so that it's a with-nlg as opposed to only-nlg

[ym-han]

@inariksit when you have time, would you be willing to test this out a bit? If it works, then the only thing that needs to be done before we can merge this would be to refactor the lens stuff in the Render module to use optics instead of lens where possible (as per the convention in the rest of the codebase). There's an example of how this can be done in Main.hs, I think, but I can also do this refactoring if you would prefer that.

[ym-han]

As noted in a comment on the PR, there are two things that should be done:

1. Some testing of my latest changes to the CLI
2. Refactor lens stuff in Render to use optics where possible (I think there's an example of this in Main.hs)

When testing, make sure that your .env includes the following lines:

COMPILED_SIMALA_OUTPUT_DIR="generated/simala"
NLG_EN_OUTPUT_DIR="generated/nlg_en"
NLG_EN_OUTPUT_FILENAME="nlg_en_output.json"
GF_PORTABLE_GRAMMAR_FORMAT_FILENAME="Lam4.pgf"

[inariksit]

@ym-han With refactoring lens to use optics, do you mean this one-liner function? https://github.com/smucclaw/lam4/blob/nlg-output/lam4-backend/src/Lam4/Render/Render.hs#L90

The most similar line in Main.hs I'm seeing is this https://github.com/smucclaw/lam4/blob/nlg-output/lam4-cli/app/Main.hs#L191 , which uses the function regex from Control.Lens.Regex.ByteString.

This is the commit in October where I switched from PCRE to Lens-regexes, would you prefer me to restore the change? f6aa458