Configure production logs to go to appsignal.

[jim]

What it does

• Configures the production logs to log in a single-line format to appsignal

Why it is important

This will make our logs more searchable and also adds a user_id property so we can see what actions a given user takes. A few times now we've needed to understand a bug report from a user and didn't have this as a diagnostic tool.

Implementation notes

• Added the lograge gem.
• In production, configured logs to go to appsignal using the logfmt format.
• The development logs and normal Rails logs that go to Heroku should remain unchanged.=

Your bandwidth for additional changes to this PR

• I have the time and interest to make additional changes to this PR based on feedback.