observability: remove default values

Created by: slimsag

Default values seem like a good idea at first glance, because it is the only way to prevent Grafana from showing "No data" (which looks like "monitoring isn't working") but in practice default values like this do not work well because when viewing a large timerange both with sections of data and no data, it produces two vectors: one with labels, and one without. I had forgotten about this and added it to the generator.

This can lead to confusing displays such as this:

"Why are there two types of 'hard error's?!"

Or this:

"What is 'HTTP code' and why when I click it does nothing show up?!"