approved configurations

WIP

This adds "configurations" and "configuration requests" as a concept.

A Configuration is a combination of observing mode, conditions, and target which are approved via ITAC and can also be approved during Phase II by special permission. A configuration only cares about certain aspects of the observing mode, conditions, and target; everything else is irrelevant to the approval process and can be changed freely at Phase II.
Every observation has a Configuration which is derived from the observation properties and may be incomplete while the observation is being defined. This is a property on type Observation and is used internally, but is probably of little use to end users.
Once a configuration is fully defined, the user can create a ConfigurationRequest, which means "please approve this configuration". Possible states are requested, approved, and denied. Requests are a property of the program.
Observations receive a warning unless there exists an approved requests that applies to it. A given configuration (and thus a given request) may apply to many observations.

Left to do in followups:

Create configuration requests for all observations when the proposal is submitted.
Provide a mutation to approve, deny, and delete requests.
Ensure that duplicate requests are not created.