Update some rocker scripts for arm64 build (and some minor improvements)

[eitsupi]

Related to #144, continuation of work of #195.

Modify the following script to work with arm64 builds.

• install_s6init.sh
• install_texlive.sh
• install_pandoc.sh

With this improvement, all software required to build rocker/verse except RStudio Server can be installed on arm64 images.

According to my research, install_wgrib2.sh cannot be executed with arm64, so rocker/geospatial will not be able to make an arm64 build even if the arm64 version of RStudio Server appears.
The survey results were added as comments in the script.

In addition, the following minor improvements have been made in this PR.

• Remove S6 installer in install_s6init.sh.
• Avoiding the error of running install_texlive.sh without the non-root user. (In most cases, it's a script that runs after installing RStudio Server and create the default user, so it hasn't been a problem until now.)
• Addition of BiocManager installation that was missing in install_geospatial.sh. (In most cases, it's a script that runs after installing BiocManager, so it hasn't been a problem until now.)
• Set -ncpus -1 argument for all install2.r commands.

[cboettig]

This looks wonderful, nice work! 🎉

(yeah, no worries about wgrib2, that's a bit niche in geospatial as you probably gathered anyhow)