* message.nim: set max message size to 150KiB according to spec
Using KiB instead of KB because that seems more aligned with
the actual default defined in nim-libp2p (1024 * 1024)
Spec details: https://rfc.vac.dev/spec/64/#message-size
* test_protocol.nim: align test to current WakuMessage limit
* test_waku_client.nim: adapt test to MaxWakuMessageSize change
* make maxMessageSize configurable for wakunode2
* wakunode2 app now accepts max-num-bytes-msg-size with KiB, KB, or B units
* testlib/wakunode.nim: set maxMessageSize: "1024 KiB"
* test_waku_client.nim: remove duplicate check in "Valid Payload Sizes"
* set DefaultMaxWakuMessageSizeStr as the only source of truth
* external_config.nim: rename max-num-bytes-msg-size -> max-msg-size
Ivan FB
Hanno Cornelius