Expose memory usage for each function execution

We should expose this since the billing is based on that. Since App Insights is the future, that would be the right place for users to see this, alongside the rest of the data about each execution (duration, logs, ...).

The issue does not name files, tests, or entry points. Start by locating the host's execution data sent to App Insights, then determine how memory usage could appear alongside duration and logs; done means users can see memory usage for each function execution.

Written by the indexing model from the issue text.