github: Run charon-tkm tests

Use a Debian-based Docker container to run the unit tests for charon-tkm,
once without and once with TKM running.  The container can also be used
locally to run the tests (see comments in the Dockerfile).

testing/tkm/generate-config.sh

@@ -0,0 +1,10 @@
+#!/bin/bash
+
+openssl genrsa -out key.pem 2048
+openssl rsa -in key.pem -outform der -out key.der
+
+openssl req -x509 -nodes -newkey rsa:4096 -keyout cakey.pem -outform der \
+	-out ca.der -sha256 -subj "/CN=CA" -addext basicConstraints=critical,CA:TRUE
+
+tkm_cfgtool -c /usr/local/share/tkm/tkm.conf -i swanctl.conf \
+	-t tkm.conf -s /usr/local/share/tkm/tkmconfig.xsd