Adds new platform for download page, "Arch Linux" and the necessary i…

[nateynateynate]

…nstructions to install via its native package manager.

Description

#642 has been sitting around for a while. I was under the impression that there was some kind of clarification that was to be added to the download instructions regarding how the opensearch package is actually opensearch-min, but I think it's sat long enough. Here's the path I took:

I added a dropdown to the OpenSearch and OpenSearch Dashboards sections of the download page to inlcude "Arch Linux" as a platform. Selecting any of the build variants will just show the command line instruction to install the opensearch package via pacman (pacman -S opensearch)

Caveats:

• The pacman package listing showed the only available architecture was x86_64, so I left out any other arch.
• I didn't see pacman packages for the earlier release line of 1.3.x so I created no download artifacts for those.

Issues Resolved

#642

Check List

• Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the BSD-3-Clause License.

[hashworks]

Selecting any of the build variants will just show the command line instruction to install the opensearch package via pacman (pacman -S opensearch)

As long as this doesn't confuse users since they need to install plugins via other packages.

The pacman package listing showed the only available architecture was x86_64, so I left out any other arch.

Correct, we currently only provide x86_64. Others are planned (f.e. x86_64_v3, arm64), but this will take a while.

I didn't see pacman packages for the earlier release line of 1.3.x so I created no download artifacts for those.

Also correct, Arch Linux will only ever provide the latest version of opensearch.

[dtaivpp]

Lgtm