FEATURE: Set default values for Commons fields in application.properties / env variables

[github-actions[bot]]

Priority issue

Worth 20 points when fully complete.

User Story

• As a developer
• I can set the default values for commons fields in application.properties, and/or via env variables
• So that as/when instructors find different defaults are useful, we can set those without having to change code

Discussion

Currently the following values for a new commons have defaults that are hard coded:

• Starting Balance
• Cow Price
• Milk Price
• Degradation Rate
• Carrying Capacity
• Health Update Formula When Above Capacity
• Health Update Formula When Below Capacity

These fields don't have default values, but should:

• Capacity Per User

We would like, instead, for those default values to be settable in application.properties, and overridable by environment variables.

Value	property name	env variable
Starting Balance	app.commons.default.startingBalance	HAPPYCOWS_STARTING_BALANCE
Cow Price	app.commons.default.cowPrice	HAPPYCOWS_COW_PRICE
Milk Price	app.commons.default.milkPrice	HAPPYCOWS_MILK_PRICE
Degradation Rate	app.commons.default.degradationRate	HAPPYCOWS_MILK_PRICE
Carrying Capacity	app.commons.default.carryingCapacity	HAPPYCOWS_CARRYING_CAPACITY
Capacity Per User	app.commons.default.capacityPerUser	HAPPYCOWS_CAPACITY_PER_USER
Health Update Formula When Above Capacity	app.commons.default.aboveCapacityHealthUpdateStrategy	HAPPYCOWS_ABOVE_CAPACITY_HEALTH_UPDATE_STRATEGY
Health Update Formula When Below Capacity	app.commons.default.belowCapacityHealthUpdateStrategy	HAPPYCOWS_BELOW_CAPACITY_HEALTH_UPDATE_STRATEGY

Acceptance Criteria

• [x] Values are settable via application.properties
• [x] Values are settable via environment variable
• [ ] The README.md points to a new document docs/environment.md that explains these environment variables, and all others that can be defined in the app (including existing ones.)

Implementation

I strongly encourage you to break this into two separate PRs

First PR: Backend only (10 points)

• [x] Set up these variables in application.properties
• [x] Set up a new endpoint in commons controller called /api/commons/defaults that returns a Commons object in JSON format containing these values.

Second PR: Frontend Only (10 points)

Frontend:

• [ ] On the commons create page, get the default values from /api/commons/defaults and pre-populate the form with those values instead of using hard coded values.