[scd] Validate Volume4D when parsing

[RustedBones]

Factorize validation for Volume3D and Volume4D during parsing:

• Ensure startTime < endTime when defined
• Ensure altLo < altHi when defined

Introduce parsing options to tune validation:

• Ensure altLo and altHi set when RequireAltitudeBounds enabled
• Ensure startTime ans endTime set when RequireTimeBounds enabled

Configuration options for SCD entities mutation:

• op-intent: RequireTimeBounds: true, RequireAltitudeBounds: true
• constraints: RequireTimeBounds: true, RequireAltitudeBounds: false
• subscriptions: RequireTimeBounds: false, RequireAltitudeBounds: false

For SCD queries: RequireTimeBounds: false, RequireAltitudeBounds: false

[mickmis]

Intent SGTM, I do have suggestions regarding implementation, please LMK what you think.

[mickmis]

Using something inspired from the options/builder patterns could provide a cleaner and extensible interface here, i.e. sth like:

type Volume4DValidator func(*Volume4D) error

func WithRequireTimeBounds() Volume4DValidator {
    return func(v *Volume4D) {
        if v.StartTime == nil {
            return fmt.Errorf("no start time")
        }
        if v.EndTime == nil {
            return fmt.Errorf("no end time")
        }
    }
}

func Volume4DFromSCDRest(vol4 *restapi.Volume4D, validators ...Volume4DValidator) (*Volume4D, error) {
    ...
    for _, validator := range validators {
        if err := validator(svc); err != nil {
            ...
        }
    }
    ...
}

[mickmis]

Do we actually ever need to validate those directly on a Volume3D? If not consider doing the validation only from Volume4DFromSCDRest.