Improve tx pool logging in RPC when then pool is not enabled or node not in sync. (#7106)

* update tx pool logging when not enabled.

Signed-off-by: Matt Nelson <85905982+non-fungible-nelson@users.noreply.github.com>

* Spotless

Signed-off-by: Matt Nelson <85905982+non-fungible-nelson@users.noreply.github.com>

* better wording

Co-authored-by: Sally MacFarlane <macfarla.github@gmail.com>
Signed-off-by: Matt Nelson <85905982+non-fungible-nelson@users.noreply.github.com>

---------

Signed-off-by: Matt Nelson <85905982+non-fungible-nelson@users.noreply.github.com>
Co-authored-by: Sally MacFarlane <macfarla.github@gmail.com>

ethereum/api/src/main/java/org/hyperledger/besu/ethereum/api/jsonrpc/internal/response/RpcErrorType.java

@@ -33,7 +33,9 @@ public enum RpcErrorType implements RpcMethodError {
   METHOD_NOT_ENABLED(-32604, "Method not enabled"),
 
   // Resource unavailable error
-  TX_POOL_DISABLED(-32002, "Transaction pool not enabled"),
+  TX_POOL_DISABLED(
+      -32002,
+      "Transaction pool not enabled. (Either txpool explicitly disabled, or node not yet in sync)."),
 
   // eth_getBlockByNumber specific error message
   UNKNOWN_BLOCK(-39001, "Unknown block"),