chore: add code owners (#784)

Through Github rulesets and the definition of code owners, it is possible to automate the review
process without additional workflows. It also makes responsibilities within the project clearer. The
current CODEOWNERS file is very simple but more complex rules can be introduced in the future.

re #783

Author: cedoor

.github/CODEOWNERS

@@ -0,0 +1 @@
+*       @semaphore-protocol/core-devs