Update build script

[MAFLO321]

Hi,
first of all, this is a totally awesome project! I also run my pbs on an Armbian64 system 😄.
Thanks for the build script and patches 🥳.

What I have changed:

• use commands listed in rust docs
  • Updated the commands as shown in the docs for a more secure download.
• add more missing dependencies
  • While trying to build the project in a clean chroot (debootstrap --variant=buildd bullseye ${CHROOTDIR} http://deb.debian.org/debian/) I observed that the following packages are also needed:
    • libpam0g-dev by proxmox-backup
    • libcurl4-openssl-dev by pve-xtermjs
• cleanup build path args and always install build-deps and copy all packages back
  • use (hopefully it was your intention 😉) convention for using a tailing-/ after each path
  • install at every package the needed build-deps (except for proxmox-acme, see comment)
  • sort the variables with the commit ids and use XXX_VER for the version (I'm also not sure what your intention was, hopefully that was your intention. But I think XXX_VERSION would also look good or even better, what do you think?)
  • copy all needed packages for an installation on another host and also include the debugging symbol packages (maybe someone needs them some time)
• refactor git operations
  • extract two functions, for git operations that are performed several times
  • maybe combine the two functions into a third one, so that only one call per repo would be necessary?
• use variables for paths and move sources into subfolder
  • move all the downloaded sources into a subfolder called sources (I was not sure what's better build or sources, what do you think?)
  • create variables containing absolute paths to often used folders for better handling
  • maybe also the cd <project> and cd .. could also be replaced by cd ${SOURCES}/<project> and cd ${SOURCES} or/and replace cd with pushd/popd ... I was not sure for now I think it is ok as it is.
• add .gitignore

Feedback is welcome!
I will integrate everything you think should be changed or is not good, just let me know.

[wofferl]

Thanks for your contribution, looks good to me.