Update pfcp-agent

To the same version tested with up4 contained in sdfabric-onos image:

    docker image inspect opennetworking/sdfabric-onos:master-2022-02-07 | grep org.omecproject.up4.version
        "org.omecproject.up4.version": "59857a4b0cbe7f2e0a71128929860db5a082bc0b",

    https://github.com/omec-project/up4/blob/59857a4b0cbe7f2e0a71128929860db5a082bc0b/.env.stable#L5

Change-Id: If311ede57e675654a0a66fdc98683ccd92910d0c
diff --git a/VERSION b/VERSION
index 140333f..c2320f5 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-1.0.19
+1.0.20