chore: added missing CODEOWNERS file

The CODEOWNERS file was missing, adding with the two initial teams:
* maintainers
* web

Signed-off-by: Jonathan Gonzalez V. <jonathan.abdiel@gmail.com>

Author: sxd

CODEOWNERS

@@ -0,0 +1,8 @@
+# The CODEOWNERS file is used to define individuals or teams that are
+# responsible for code in a repository. For details, please refer to
+# https://docs.github.com/en/free-pro-team@latest/github/creating-cloning-and-archiving-repositories/about-code-owners
+
+* @cloudnative-pg/maintainers
+
+# Website team
+* @cloudnative-pg/web