Metric Definitions: Added metric definitions endpoints + reponse bodies

[RobGeada]

1. The OpenAPI specification now has short metric descriptions in the tags:

openapi: 3.0.3
info:
  title: trustyai-service API
  version: 1.0.0-SNAPSHOT
tags:
- name: Disparate Impact Ratio Endpoint
  description: Disparate Impact Ratio (DIR) measures imbalances in classifications
    by calculating the ratio between the proportion of the majority and protected
    classes getting a particular outcome.
- name: Statistical Parity Difference Endpoint
  description: Statistical Parity Difference (SPD) measures imbalances in classifications
    by calculating the difference between the proportion of the majority and protected
    classes getting a particular outcome.

2. General metric definitions can be queried by:
   curl -X GET http://localhost:8080/metrics/spd/definition
   returns
   Statistical Parity Difference (SPD) measures imbalances in classifications by calculating the difference between the proportion of the majority and protected classes getting a particular outcome. Typically, -0.1 < SPD < 0.1 indicates a fair model, while a value outside those bounds indicates an unfair model for the groups and outcomes in question.

3. Specific metric descriptions are returned in metric query bodies:

curl -X POST --location "http://localhost:8080/metrics/dir/" \
    -H "Content-Type: application/json" \
    -d "{
          \"protectedAttribute\": \"gender\",
          \"favorableOutcome\": 1,
          \"outcomeName\": \"income\",
          \"privilegedAttribute\": 1,
          \"unprivilegedAttribute\": 0
        }"

returns
{"type":"metric","name":"DIR","value":0.17292587250695893,"specificDefinition":"The DIR of 0.172926 indicates that the likelihood of Group:gender=1 receiving Outcome:income=1 is 0.172926 times that of Group:gender=0.","id":"2b3e009a-ddf7-496e-843d-812893c3a478","timestamp":"2023-02-13T13:42:03.448+00:00","thresholds":{"lowerBound":0.8,"upperBound":1.2,"outsideBounds":true}}

[danielezonca]

CI is broken until this PR is merged

• Metric Definitions: Add plaintext fairness metric definitions for spd + dir trustyai-explainability#57