Start milestone 3

- Add functionality to query online sources (Keyservers, etc) for
  certificates.
- Use introducers to determine which UserIDs should be fetched from
  online soources. Check certifications before importing certifiactes
  into the local cert store.
- start docker image for local end-to-end testing.

docker/mta_provision/opt/husk/config.toml

@@ -0,0 +1,7 @@
+connection = "localhost:3000"
+
+sequoia_home = "/tmp/sq_home"
+
+logfile_config = "./log4rs.yml"
+
+keyservers = [ "hkps://example.com" ]

docker/mta_provision/opt/husk/log4rs.yml

@@ -0,0 +1,17 @@
+appenders:
+  stdout_appender:
+    kind: console
+    encoder:
+      pattern: "{h({d(%Y-%m-%d %H:%M:%S)(utc)} - {l}: {m}{n})}"
+
+  file_appender:
+    kind: file
+    path: "/tmp/husk.log"
+    encoder:
+      pattern: "{h({d(%Y-%m-%d %H:%M:%S)(utc)} - {l}: {m}{n})}"
+
+root:
+  level: debug
+  appenders:
+    - file_appender
+