[docs] [R-package] upgrade R documentation to {pkgdown} 2.0

[jameslamb]

Summary

This project uses {pkgdown} to generate a documentation website for the R package (https://lightgbm.readthedocs.io/en/latest/R/reference/).

A new major release of {pkgdown}, v2.0, was recently published to CRAN (link) and to conda-forge (link).

This project's documentation should be updated to use that new version of {pkgdown}.

Motivation

This release brings some significant new features, detailed at https://www.tidyverse.org/blog/2021/12/pkgdown-2-0-0.

I think the following would be useful for {lightgbm}:

• ability to specify redirects when pages are removed (extra important now that progress is being made on [R-package] Rewrite R demos, replace with vignettes #1944)
• static site search with no external dependencies

Description

To implement this, update the conda environment used in readthedocs ("RTD") builds so that it uses pkgdown>=2.0.0.

LightGBM/docs/conf.py

Lines 262 to 275 in f7e3938

	/home/docs/.conda/bin/conda create \
	-q \
	-y \
	-c conda-forge \
	--override-channels \
	-n r_env \
	r-base=4.1.0=hb67fd72_2 \
	r-data.table=1.14.0=r41hcfec24a_0 \
	r-jsonlite=1.7.2=r41hcfec24a_0 \
	r-knitr=1.35=r41hc72bb7e_0 \
	r-matrix=1.3_4=r41he454529_0 \
	r-pkgdown=1.6.1=r41hc72bb7e_0 \
	r-rmarkdown=2.11=r41hc72bb7e_0 \
	r-roxygen2=7.1.1=r41h03ef668_0

And possibly make changes to the configuration in https://github.com/microsoft/LightGBM/tree/f7e39388d0327e687854f22d7e06aec302770994/R-package/pkgdown.

References

{pkgdown} repo: https://github.com/r-lib/pkgdown

Vignette explaining how to add search to a {pkgdown} site: https://cran.r-project.org/web/packages/pkgdown/vignettes/search.html

[jameslamb]

Per this project's policy, I've added this feature request to #2302. Anyone is welcome to contribute this! If you're interested, please comment here. The issue can be re-opened and maintainers will be happy to answer any questions you have.

[jameslamb]

Sorry, this was locked accidentally. Just unlocked it. We'd still love help with this feature!