feat(synapse_signing_key): add ansible module for managing signing keys

plugins/modules/synapse_signing_key.md

@@ -0,0 +1,33 @@
+# `finallycoffee.matrix.synapse_signing_key` module
+
+Module to generate and manage synapse signing keys.
+
+> [!TIP]
+> Supports `check mode` and `diff` rendering
+
+## Requirements
+
+- `python >= 3.9`
+- `signed_json >= 1.1.4`
+
+
+## Usage examples
+
+```yaml
+# Generate a key
+- finallycoffee.matrix.synapse_signing_key:
+    path: "/not/there/yet/signing.key"
+    state: present
+
+# Read a key from the filesystem or generate one
+- finallycoffee.matrix.synapse_signing_key:
+    path: "/maybe/existing/signing/key"
+  register: key_result
+- debug:
+    msg: "Signing key is '{{ key_result.signing_key }}'"
+
+# Delete an existing signing key file
+- finallycoffee.matrix.synapse_signing_key:
+    path: "/path/to/key/to/delete.key"
+    state: absent
+```