Add codeowners (#559)

Co-authored-by: Eric Lau <ericglau@outlook.com>

Author: heap-coder

.github/CODEOWNERS

@@ -0,0 +1,12 @@
+# Path Owners
+* @OpenZeppelin/wizard
+/packages/core/solidity @OpenZeppelin/contracts @OpenZeppelin/wizard
+/packages/ui/src/solidity @OpenZeppelin/contracts @OpenZeppelin/wizard
+/packages/core/cairo @OpenZeppelin/cairo @OpenZeppelin/wizard
+/packages/core/cairo_alpha @OpenZeppelin/cairo @OpenZeppelin/wizard
+/packages/ui/src/cairo @OpenZeppelin/cairo @OpenZeppelin/wizard
+/packages/ui/src/cairo_alpha @OpenZeppelin/cairo @OpenZeppelin/wizard
+/packages/core/stylus @OpenZeppelin/stylus @OpenZeppelin/wizard
+/packages/ui/src/stylus @OpenZeppelin/stylus @OpenZeppelin/wizard
+/packages/core/stellar @OpenZeppelin/stellar @OpenZeppelin/wizard
+/packages/ui/src/stellar @OpenZeppelin/stellar @OpenZeppelin/wizard