docs(validator): include more complete examples & intro to JSON Schema (aws-powertools#389)

* docs(validation): use new structure

* docs(validation): include complete examples

Author: heitorlessa

docs/shared/validation_basic_eventbridge_event.json

@@ -0,0 +1,15 @@
+{
+    "id": "cdc73f9d-aea9-11e3-9d5a-835b769c0d9c",
+    "detail-type": "Scheduled Event",
+    "source": "aws.events",
+    "account": "123456789012",
+    "time": "1970-01-01T00:00:00Z",
+    "region": "us-east-1",
+    "resources": [
+        "arn:aws:events:us-east-1:123456789012:rule/ExampleRule"
+    ],
+    "detail": {
+        "message": "hello hello",
+        "username": "blah blah"
+    }
+}

docs/shared/validation_basic_jsonschema.py

@@ -0,0 +1,39 @@
+INPUT = {
+    "$schema": "http://json-schema.org/draft-07/schema",
+    "$id": "http://example.com/example.json",
+    "type": "object",
+    "title": "Sample schema",
+    "description": "The root schema comprises the entire JSON document.",
+    "examples": [{"message": "hello world", "username": "lessa"}],
+    "required": ["message", "username"],
+    "properties": {
+        "message": {
+            "$id": "#/properties/message",
+            "type": "string",
+            "title": "The message",
+            "examples": ["hello world"],
+            "maxLength": 100,
+        },
+        "username": {
+            "$id": "#/properties/username",
+            "type": "string",
+            "title": "The username",
+            "examples": ["lessa"],
+            "maxLength": 30,
+        },
+    },
+}
+
+OUTPUT = {
+    "$schema": "http://json-schema.org/draft-07/schema",
+    "$id": "http://example.com/example.json",
+    "type": "object",
+    "title": "Sample outgoing schema",
+    "description": "The root schema comprises the entire JSON document.",
+    "examples": [{"statusCode": 200, "body": "response"}],
+    "required": ["statusCode", "body"],
+    "properties": {
+        "statusCode": {"$id": "#/properties/statusCode", "type": "integer", "title": "The statusCode"},
+        "body": {"$id": "#/properties/body", "type": "string", "title": "The response"},
+    },
+}