feat: validate rln relay config when mounting

Fails faster when ethereum client address is not passed.

waku/node/waku_node.nim

@@ -1046,6 +1046,11 @@ proc mountRlnRelay*(
 ) {.async.} =
   info "mounting rln relay"
 
+  let validationRes = rlnConf.validate()
+  if validationRes.isErr():
+    echo "it is ERR"
+    raise newException(CatchableError, validationRes.error)
+
   if node.wakuRelay.isNil():
     raise newException(
       CatchableError, "WakuRelay protocol is not mounted, cannot mount WakuRlnRelay"

waku/waku_rln_relay/rln_relay.nim

@@ -45,6 +45,11 @@ type WakuRlnConfig* = object
   onFatalErrorAction*: OnFatalErrorHandler
   rlnRelayUserMessageLimit*: uint64
 
+proc validate*(rlnConfig: WakuRlnConfig): Result[void, string] =
+  if rlnConfig.rlnRelayEthClientAddress == "":
+    return err("Rln Relay Eth Client address must be specified")
+  ok()
+
 proc createMembershipList*(
     rln: ptr RLN, n: int
 ): RlnRelayResult[(seq[RawMembershipCredentials], string)] =