feat: add installation scripts

[consideRatio]

Add inspectable Unix and Windows install scripts, document cautious
and convenience install paths, and add a workflow that tests the
scripts against fake release archives.

Signed-off-by: Erik Sundell erik.sundell@sensmetry.com

---

I think it could be fine to put this higher up in the docs about installation, but figured its freshly introduced and not tested properly yet, so it could be better left below other install options for now.

I'm looking land this tomorrow and write trusted publishing docs with examples making use of it in CI context.

Instead of providing this example, it would become:

      - name: Install sysand
        run: |
          ARCH=$(uname -m | sed 's/aarch64/arm64/')
          SYSAND_VERSION=$(
            curl -fsSL https://api.github.com/repos/sensmetry/sysand/releases \
              | awk -F'"' '/"tag_name":/ { tag=$4 } /"prerelease": true/ && !found { found=tag } END { if (found) print found }'
          )
          SYSAND_ARCHIVE="sysand-linux-${ARCH}.tar.xz"
          curl -fsSL "https://github.com/sensmetry/sysand/releases/download/${SYSAND_VERSION}/sysand-linux-${ARCH}.tar.xz" \
            | tar -xJ sysand
          install -m 0755 sysand /usr/local/bin/sysand
          sysand --version

      - name: Install sysand
        run: |
          curl -fsSL https://client.sysand.com/install.sh | sh

• fixes Provide installer scripts (.sh / .ps1) #367

[consideRatio]

Rebased and force-pushed.