Add age plugin support

See https://github.com/str4d/rage/tree/main/age-plugin.

Example usage:

	RAGE_DIR=$PWD/../Rust/rage
	(cd $RAGE_DIR; cargo build --all)
	export PATH=$PATH:$RAGE_DIR/target/debug

	age-plugin-trezor -i "John Doe" | tee trezor.id
	R=$(grep recipient trezor.id | cut -f 3 -d ' ')

	date | tee msg.txt
	rage -er $R < msg.txt > enc.txt
	rage -di trezor.id < enc.txt

agents/trezor/setup.py

@@ -37,5 +37,6 @@ setup(
         'trezor-gpg = trezor_agent:gpg_tool',
         'trezor-gpg-agent = trezor_agent:gpg_agent',
         'trezor-signify = trezor_agent:signify_tool',
+        'age-plugin-trezor = trezor_agent:age_tool',  # see https://github.com/str4d/rage/blob/main/age-plugin/README.md
     ]},
 )