Add AppStream metainfo for Helium

[koyuawsmbrtn]

For your pull request to not get closed without review, please confirm that:

• An issue exists where the maintainers agreed that this should be implemented.
  If such issue did not exist before, I opened one. [FR]: AppStream Metadata #220
• I tested that my contribution works locally, and does not break anything,
  otherwise I have marked my PR as draft.
• If my contribution is non-trivial, I did not use AI to write most of it.
• I understand that I will be permanently banned from interacting with this
  organization if I lied by checking any of these checkboxes.
• The pull request contents are only relevant to the Linux platform, and can in
  no way be applied to other platforms.

---

Adds AppStream metadata so Helium properly shows up in GUI package managers using PackageKit. Currently unfinished: needs screenshots and works with RPMs only (I think that's the only ones we build so far?). This is my first pull request to this repository, so please be nice to me.

[greptile-apps]

_{Last reviewed commit: 0f2dc28}

[dumbmoron]

@greptileai

[greptile-apps]

_{Last reviewed commit: 3bd9f7b}

[dumbmoron]

copr build is failing: https://download.copr.fedorainfracloud.org/results/imput/helium/srpm-builds/10233256/builder-live.log.gz

RPM build warnings:

RPM build errors:
stderr: warning: Downloading https://github.com/imputnet/helium-linux/releases/download/0.10.5.1/helium-0.10.5.1-x86_64_linux.tar.xz to /var/lib/copr-rpmbuild/results/helium-0.10.5.1-x86_64_linux.tar.xz
warning: Downloading https://github.com/imputnet/helium-linux/releases/download/0.10.5.1/helium-0.10.5.1-arm64_linux.tar.xz to /var/lib/copr-rpmbuild/results/helium-0.10.5.1-arm64_linux.tar.xz
error: Bad file: /var/lib/copr-rpmbuild/results/net.imput.helium.metainfo.xml: No such file or directory
    Downloading https://github.com/imputnet/helium-linux/releases/download/0.10.5.1/helium-0.10.5.1-x86_64_linux.tar.xz to /var/lib/copr-rpmbuild/results/helium-0.10.5.1-x86_64_linux.tar.xz
    Downloading https://github.com/imputnet/helium-linux/releases/download/0.10.5.1/helium-0.10.5.1-arm64_linux.tar.xz to /var/lib/copr-rpmbuild/results/helium-0.10.5.1-arm64_linux.tar.xz
    Bad file: /var/lib/copr-rpmbuild/results/net.imput.helium.metainfo.xml: No such file or directory

Copr build error: warning: Downloading https://github.com/imputnet/helium-linux/releases/download/0.10.5.1/helium-0.10.5.1-x86_64_linux.tar.xz to /var/lib/copr-rpmbuild/results/helium-0.10.5.1-x86_64_linux.tar.xz
warning: Downloading https://github.com/imputnet/helium-linux/releases/download/0.10.5.1/helium-0.10.5.1-arm64_linux.tar.xz to /var/lib/copr-rpmbuild/results/helium-0.10.5.1-arm64_linux.tar.xz
error: Bad file: /var/lib/copr-rpmbuild/results/net.imput.helium.metainfo.xml: No such file or directory
    Downloading https://github.com/imputnet/helium-linux/releases/download/0.10.5.1/helium-0.10.5.1-x86_64_linux.tar.xz to /var/lib/copr-rpmbuild/results/helium-0.10.5.1-x86_64_linux.tar.xz
    Downloading https://github.com/imputnet/helium-linux/releases/download/0.10.5.1/helium-0.10.5.1-arm64_linux.tar.xz to /var/lib/copr-rpmbuild/results/helium-0.10.5.1-arm64_linux.tar.xz
    Bad file: /var/lib/copr-rpmbuild/results/net.imput.helium.metainfo.xml: No such file or directory