MAINTAINERS: Add myself as CoAP collaborator

Add myself as collaborator for CoAP related code.

Signed-off-by: Pieter De Gendt <pieter.degendt@basalte.be>
diff --git a/MAINTAINERS.yml b/MAINTAINERS.yml
index 8c3df33..9d9db39 100644
--- a/MAINTAINERS.yml
+++ b/MAINTAINERS.yml
@@ -1150,6 +1150,8 @@
     status: maintained
     maintainers:
         - rlubos
+    collaborators:
+        - pdgendt
     files:
         - subsys/net/lib/coap/
         - samples/net/sockets/coap_*/