Add CODEOWNERS to the repmgr repo

Signed-off-by: Martín Marqués <martin.marques@enterprisedb.com>

.github/CODEOWNERS

@@ -0,0 +1,7 @@
+# Each line is a file pattern followed by one or more owners.
+
+# These owners will be the default owners for everything in
+# the repo. Unless a later match takes precedence,
+# @global-owner1 and @global-owner2 will be requested for
+# review when someone opens a pull request.
+*       @EnterpriseDB/repmgr-dev