build: include LICENSE.txt in all artifacts (#4630)

Adds our LICENSE file as LICENSE.txt to our binary .zip files,
Docker containers, and RPM files.

.github/workflows/build.yml

@@ -261,6 +261,11 @@ jobs:
         with:
           name: ${{ env.PKG_NAME }}_${{ needs.set-product-version.outputs.product-version }}_${{ matrix.goos }}_${{ matrix.goarch }}.zip
           path: out/${{ env.PKG_NAME }}_${{ needs.set-product-version.outputs.product-version }}_${{ matrix.goos }}_${{ matrix.goarch }}.zip
+      - name: Copy license file to config_dir
+        env:
+          LICENSE_DIR: ".release/linux/package/usr/share/doc/${{ env.PKG_NAME }}"
+        run: |
+          mkdir -p "$LICENSE_DIR" && cp LICENSE "$LICENSE_DIR/LICENSE.txt"
       - name: Package
         uses: hashicorp/actions-packaging-linux@v1  # TSCCR: loading action configs: failed to query HEAD reference: failed to get advertised references: authorization failed
         with: