[REQ] Restyle R code

Hi @wing328 !

I'm looking into submitting an R package (laminr.api) generated by openapi-generator to CRAN.

There a few things that I think CRAN will comment on when I submit the package.

I'd like to make a couple of changes to the mustache templates for R to fix a couple of issues:

• Small code style changes (e.g. using <- instead of = or seq_along(x) instead of 1:length(x))
• Fix some issues with the roxygen docs (I get warnings like default_api.R:2961: @param requires two parts: an argument name and a description. when running devtools::document() so there are some minor things that need to be fixed)
• Fix discrepancies between the httr and httr2 API client -- I see some slight differences in the way that the httr and httr2 versions are being rendered; would it make sense to align their mustache templates a little bit

I'll make sure to not modify the interface of the package as not to break anything for existing packages.

@wing328 : Is it okay if I send a couple of PRs your way? Would you prefer if send one big PR which you can review the changes all at once, or that I try to split up the work into multiple PRs which can reviewed separately?

Also @wing328: do you know of any other R packages that are already on CRAN that were generated by this generator?

Thanks for your input!
Robrecht

Locate the R mustache templates that render the httr and httr2 clients, then compare their generated output. Check the style changes and roxygen warnings by running devtools::document() on the generated package. Done means the generated R code follows the requested style, documentation warnings are fixed, the client renderings are aligned where appropriate, and the package interface is unchanged.