pull the password out of the file

I know it's still in the store, which I'm not *super* happy about... but I
don't see a better way of doing this. I have bcrypted it locally, though,
which Concourse allows.

.gitignore

@@ -1,4 +1,5 @@
 /gitea/backups-*.key
+/gitea/concourse_password
 /gitea/result
 /gitea/smtp_password
 /result

gitea/configuration.nix

@@ -220,7 +220,8 @@ in {
       ];
       environment = {
         CONCOURSE_CLUSTER_NAME = "bytes.zone";
-        CONCOURSE_ADD_LOCAL_USER = "brian:test";
+        CONCOURSE_ADD_LOCAL_USER =
+          "brian:${builtins.readFile ./concourse_password}";
         CONCOURSE_MAIN_TEAM_LOCAL_USER = "brian";
         CONCOURSE_EXTERNAL_URL = "https://ci.bytes.zone";