Generate API Token

Wrote function that generates a tailscale API token from our client id
and client secret values that we have. Have checked with the logs on
tailscale and can see that it is indeed generating the keys. This can be
considered a solution to issue #6.

src/types.rs

@@ -0,0 +1,4 @@
+pub struct ClientAuth {
+    pub id: String,
+    pub secret: String,
+}