fix: add required validation to if lesssons (#180) (#181)

* fix: add `required` validation to `if` lesssons (#180)

Closes #180

This commit adds the `required` validation on the properties that have
an `if` applicator condition applied to them in the *instructions* for
the following lessons:

-
[05-Conditional-Validation/04-if-then-keyword](https://tour.json-schema.org/content/05-Conditional-Validation/04-if-then-keyword)
-
[https://tour.json-schema.org/content/05-Conditional-Validation/06-Expanding-If-then-else](https://tour.json-schema.org/content/05-Conditional-Validation/06-Expanding-If-then-else)

* fix: move the `required` validation to the `if` schema

This commit moves the `required` validation for the example schema in
ch05's lesson "Expanding If-then-else" and places it in the `if`
subschema, so that it applies only for the purpose of the condition.

Author: eitamal

content/05-Conditional-Validation/04-if-then-keyword/instructions.mdx

@@ -29,7 +29,7 @@ You can use the `if-then` keyword to enforce this condition.
 {
   "type": "object",
   "properties": {...},
-  "if": {"properties": {"isFullTime": {"const": true}}},
+  "if": {"properties": {"isFullTime": {"const": true}}, "required": ["isFullTime"]},
   "then": {"required": ["salary"]},
 }
 ```

content/05-Conditional-Validation/06-Expanding-If-then-else/instructions.mdx

@@ -41,7 +41,8 @@ Using the `not` keyword with the `if-else` keyword can look something like this:
   "if": { 
     "properties": {
        "status": { "const": "employed" } 
-    } 
+    }, 
+    "required": ["status"]
   },
   "then": { 
     "not": { "required": ["unemploymentBenefits"] 
@@ -70,4 +71,4 @@ You are given the [schema](https://json-schema.org/learn/glossary#schema) for th
 - **If** `grade` is **greater that or equal to 8**, **then** the `recommendationLetter` field must be present, and the `personalStatement` field must **NOT** be present.
 - Else if `grade` is **lower than 8**, **then** the `personalStatement` field must be present, and the `recommendationLetter` field must **NOT** be present..
 
-> **Hint:** Use the `minimum` keyword to specify the constraint of greater than or equal to 8.
+> **Hint:** Use the `minimum` keyword to specify the constraint of greater than or equal to 8.