The script adds lines to the .bashrc to:
- retrieve the build environment for openrety
- adding the bin directory to the PATH, where a script was placed
- provide a help message

This script now just builds openresty and saves some variables that will
be useful during development, namely the RESTY_CONFIG_OPTIONS and the
PATH where luajit has been installed.

Do not install any more needed packages, which are already installed
by a previous setup step run as root.

Upgrade Openresty version to 1.19.9.1.

Enable the `--with-compat` configuration option, so that other dynamic
modules can be integrated without recompiling everything.

Remove the `--with-dtrace-probes`, which is not supported any more.

Do not consider the possibility to use non-system versions of PCRE,
ZLIB and OpenSSL.

Do not touch the .bashrc, which is done by another script, so that this
script could possibly not be run.

This is part of a restructuring of the docker image setup, in particular
to separate actions done as root from actions done as a user