feat: build and sign RPM packages

Passing files to Dom0 is always dangerous:

- Passing a git repository is dangerous as it can have ignored modified
  files and signature verification will pass.
- Passing an archive is troublesome for updates.
- Passing an RPM package depends on the RPM verification to be correct,
  some times it is not.
- Passing a RPM repository definition is less troublesome for the user,
  as it is a small file to verify the contents and update mechanism is
  via the package manager. Trust in RPM verification is still required.

Many improvements were made to the build scripts:

- requires-program: Single function to check if program is installed;
- spec-get: Sort project names for the usage message;
- spec-get: Only running commands that are necessary;
- spec-get: Fix empty summary when readme has copyright header;
- spec-gen: Fix grep warning of escaped symbol;
- spec-build: Sign RPM and verify signature;
- spec-build: Only lint the first SPEC for faster runtime;
- yumrepo-gen: Generate a local yum repository with signed metadata;
- qubesbuilder-gen: Generate a .qubesbuilder based on tracked projects;
- release: Build, sign and push all RPMs to repository.

Goal is to be able to build with qubes-builderv2 Qubes Executor.

For: https://github.com/ben-grande/qusal/issues/37

scripts/requires-program.sh

@@ -0,0 +1,19 @@
+#!/bin/sh
+## SPDX-FileCopyrightText: 2024 Benjamin Grande M. S. <ben.grande.b@gmail.com>
+##
+## SPDX-License-Identifier: AGPL-3.0-or-later
+
+set -eu
+
+missing_program=0
+for pkg in "${@}"; do
+  if ! command -v "${pkg}" >/dev/null; then
+    missing_program=1
+    echo "Missing program: ${pkg}" >&2
+    continue
+  fi
+done
+
+if test "${missing_program}" = "1"; then
+  exit 1
+fi