Add gpg_fingerprint lookup and filter (#639)

* Add gpg_fingerprint lookup.

* Work around problems on some CI targets.

* Use get_bin_path to find the gpg executable. Document that we need it.

* Improve and test error handling.

* Refactor (potentially) common code to module_utils and plugin_utils.

This will be useful to create a filter version of this, and further lookups, filters, and modules.

* Do not create a keyring when there isn't one.

* Fixups.

* Fix description.

* More fixes for lookup.

* Also add a gpg_fingerprint filter.

* Improve formulation.

Co-authored-by: Sandra McCann <samccann@redhat.com>

---------

Co-authored-by: Sandra McCann <samccann@redhat.com>

plugins/lookup/gpg_fingerprint.py

@@ -0,0 +1,64 @@
+# -*- coding: utf-8 -*-
+# Copyright (c) 2023, Felix Fontein <felix@fontein.de>
+# GNU General Public License v3.0+ (see LICENSES/GPL-3.0-or-later.txt or https://www.gnu.org/licenses/gpl-3.0.txt)
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+from __future__ import (absolute_import, division, print_function)
+__metaclass__ = type
+
+DOCUMENTATION = """
+name: gpg_fingerprint
+short_description: Retrieve a GPG fingerprint from a GPG public or private key file
+author: Felix Fontein (@felixfontein)
+version_added: 2.15.0
+description:
+  - "Takes a list of filenames pointing to GPG public or private key files. Returns the fingerprints for each of these keys."
+options:
+  _terms:
+    description:
+      - A path to a GPG public or private key.
+    type: list
+    elements: path
+    required: true
+requirements:
+  - GnuPG (C(gpg) executable)
+seealso:
+  - plugin: community.crypto.gpg_fingerprint
+    plugin_type: filter
+"""
+
+EXAMPLES = """
+- name: Show fingerprint of GPG public key
+  ansible.builtin.debug:
+    msg: "{{ lookup('community.crypto.gpg_fingerprint', '/path/to/public_key.gpg') }}"
+"""
+
+RETURN = """
+  _value:
+    description:
+      - The fingerprints of the provided public or private GPG keys.
+      - The list has one entry for every path provided.
+    type: list
+    elements: string
+"""
+
+from ansible.plugins.lookup import LookupBase
+from ansible.errors import AnsibleLookupError
+from ansible.module_utils.common.text.converters import to_native
+
+from ansible_collections.community.crypto.plugins.module_utils.gnupg.cli import GPGError, get_fingerprint_from_file
+from ansible_collections.community.crypto.plugins.plugin_utils.gnupg import PluginGPGRunner
+
+
+class LookupModule(LookupBase):
+    def run(self, terms, variables=None, **kwargs):
+        self.set_options(direct=kwargs)
+
+        try:
+            gpg = PluginGPGRunner(cwd=self._loader.get_basedir())
+            result = []
+            for path in terms:
+                result.append(get_fingerprint_from_file(gpg, path))
+            return result
+        except GPGError as exc:
+            raise AnsibleLookupError(to_native(exc))