feat(supported-version): validate custom_versions

Previously, @danslo reported that he tried to use `custom_versions` without
setting the kind. This isn't the correct behavior.
I've added a validator to alert him of this.

supported-version/src/kind/validations/custom-versions-validator.ts

@@ -0,0 +1,8 @@
+import { KindValidator } from "../validator";
+
+export const customVersionsValidator: KindValidator = (kind, customVersions) => {
+    if(customVersions && kind !== 'custom') {
+        throw new Error('`custom_versions` can only be used with kind `custom`'); 
+    }
+    return true;
+}

supported-version/src/kind/validations/is-known-kind.ts

@@ -0,0 +1,11 @@
+import { KNOWN_KINDS, Kind } from "../kinds";
+
+export const isKnownKind = (kind: Kind): boolean => {
+    if(!(kind in KNOWN_KINDS)) {
+        throw new Error(
+            `Invalid kind provided, supported kinds are: ${Object.keys(KNOWN_KINDS).join(', ')}`
+        );
+    }
+    
+    return true;
+};