feat: Add NoticeSchemaGenerator

[aababilov]

It is currently not plugged into cli/Main.java.

The schema generator uses Java reflection to find all notice
classes and describe their fields.

The schema generator currently exports JSON schema for the notices. It
may also export other schema formats in future (e.g., SQL-friendly
schema).

Sample output.

{
  "attribution_without_role": {
    "type": "object",
    "properties": {
      "attributionId": {
        "type": "string"
      },
      "csvRowNumber": {
        "type": "integer"
      }
    }
  },
  "block_trips_with_overlapping_stop_times": {
    "type": "object",
    "properties": {
      "blockId": {
        "type": "string"
      },
      "csvRowNumberA": {
        "type": "integer"
      },
      "csvRowNumberB": {
        "type": "integer"
      },
      "intersection": {
        "type": "string"
      },
      "serviceIdA": {
        "type": "string"
      },
      "serviceIdB": {
        "type": "string"
      },
      "tripIdA": {
        "type": "string"
      },
      "tripIdB": {
        "type": "string"
      }
    }
  },

[lionel-nj]

Thanks @aababilov, a few comments and suggestions in-line.

[aababilov]

Thanks for review!