Define enumeration for icarReproParturitionEventResource - calvingEase

[cookeac]

Currently the calvingEase attribute of icarReproParturitionEventResource.json is a string field with no definition.
There would be benefit in a consistent enumeration or score.

Splitting this issue out from the remaining discussion in #183 so that it can be addressed specifically. This will allow further research into the other topics in that issue.

Research: Would this cause a breaking change for current implementations?

[cookeac]

The ICAR Interbeef Technical Manual (2015/09) defines the following 1-5 scale for calving ease:

Score	Meaning
1	Easy, calved without assistance
2	Easy, calved with assistance
3	Difficult, extra or mechanical assistance
4	Difficult, veterinary assistance required
5	Caesarean or surgery

The ICAR Dairy recording guidelines emphasise the importance of calving ease but do not provide a list.
A "Trait Atlas" guide quotes an unspecified ICAR guideline with the following:

Score	Meaning
1	Easy, calved without assistance
2	Easy, calved with some assistance
3	Difficult, hard pulling, assistance by 2 or more persons, mechanical assistance
4	Caesarean section
5	Embryotomy

The list in #183 is broadly compatible with the Interbeef list

Score	Meaning
	Easy, without help
	Easy, with help
	Difficult, without veterinary care
	Difficult, with veterinary care
	Caesarean section

IF we are to define an enumeration, I recommend the five value list from Interbeef with the possible addition of Embryotomy (removal of a dead progeny) - although this could be represented in dairy cows with Caesarean and setting the liveProgeny and totalProgeny to indicate there is a stillborn progeny.

[cookeac]

After our discussions today, I propose the following enumeration for **calvingEase"" (by the way, this should really be parturitionEase or birthEase to cater for other species, but too late now!):

"type": "string",

"enum": [
"1-EasyUnassisted",
"2-EasyAssisted",
"3-DifficultExtraAssistance",
"4-DifficultVeterinaryCare",
"5-CaesareanOrSurgery"
]

[ahokkonen]

@cookeac I guess we don't need number prefix in values? (aka 1-EasyUnassisted -> EasyUnassisted)

[cookeac]

The number prefixes were for alignment with the Interbeef and other standards which document meaning but use numeric values. I would rather not have the number prefixes, but then additional documentation will be needed.

[ahokkonen]

The number prefixes were for alignment with the Interbeef and other standards which document meaning but use numeric values. I would rather not have the number prefixes, but then additional documentation will be needed.

It is better to have same naming convention for all enumeration values, I would prefer to have an additional documentation instead of prefixes :)