test: address self-announcement

Test that a node sends a self-announcement with its external IP to
in- and outbound peers after connection open and again sometime later.

Since the code for the test is mostly the same for addr and addrv2
messages, I opted to add a new test file instead of having duplicate
code in p2p_addr_relay.py and p2p_addrv2_relay.py.

Co-Authored-By: rkrux <rkrux.connect@gmail.com>

test/functional/test_runner.py

@@ -276,6 +276,7 @@ BASE_SCRIPTS = [
     'p2p_initial_headers_sync.py',
     'feature_nulldummy.py',
     'mempool_accept.py',
+    'p2p_addr_selfannouncement.py',
     'mempool_expiry.py',
     'wallet_importdescriptors.py',
     'wallet_crosschain.py',