Lock dependencies

Now that dependencies have mostly stabilised, it makes sense to ensure
that builds are reproducible and that container images use the same
versions of everything as those used for development.

It should also help prevent build errors due to any future breaking API
changes in async-graphql.

Author: tpoliaw

.gitignore

@@ -1,5 +1,4 @@
 /target
-Cargo.lock
 
 # Demo database and file number directories
 *.db