Add GraphQL schema (manual) and add client generation script

api/Makefile

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+.DEFAULT_GOAL := help
+
+# GraphQL
+#######
+
+.PHONY: generate_client
+generate_client: ## Generate client for the GraphQL API, from the schema in `schema/`
+	cd schema && bal graphql -i ./graphql.config.yaml -o ../../client
+
+
+# Util
+#######
+
+.PHONY: help
+help: # See: https://marmelab.com/blog/2016/02/29/auto-documented-makefile.html
+	@grep -E '^[a-zA-Z_-]+:.*?## .*$$' $(MAKEFILE_LIST) | sort | awk 'BEGIN {FS = ":.*?## "}; {printf "\033[36m%-30s\033[0m %s\n", $$1, $$2}'

api/schema/documents/geo_data.graphql

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+query DistrictAndCityByProvince($name: String!) {
+    geo {
+        province(name: $name) {
+            name {
+                name_en
+            }
+            districts {
+                name {
+                    name_en
+                }
+                cities {
+                    name {
+                        name_en
+                    }
+                }
+            }
+        }
+    }
+}

api/schema/graphql.config.yaml

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+schema: "./schema.graphql"
+documents:
+  - "./documents/geo_data.graphql"

api/schema/schema.graphql

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+type CityData {
+  name: LocalizedName!
+  district: DistrictData!
+}
+
+type DistrictData {
+  name: LocalizedName!
+  province: ProvinceData!
+  cities: [CityData!]!
+}
+
+type GeoData {
+  province(name: String!): ProvinceData!
+  district(name: String!): DistrictData!
+  city(name: String!): CityData!
+}
+
+"""
+Localized names in English, Sinhala, and Tamil.
+Names are stored with a `name_` prefix, followed
+by the respective ISO 639-1 language code.
+
+This record requires an English name, `name_en`.
+
+"""
+type LocalizedName {
+  """Name in English"""
+  name_en: String!
+
+  """Name in Tamil, தமிழ்"""
+  name_ta: String!
+
+  """Name in Sinhala, සිංහල"""
+  name_si: String!
+}
+
+type ProvinceData {
+  name: LocalizedName!
+  districts: [DistrictData!]!
+}
+
+type Query {
+  geo: GeoData!
+}
+