refactor: replace HttpClient with WebSocketClient in EthStatsService

[KYash03]

Fixes #8313

[macfarla]

when I run gw compileTestJava I get this error

Execution failed for task ':ethereum:ethstats:compileTestJava'.
> Compilation failed; see the compiler output below.
  /Users/sm/workspace/b2/ethereum/ethstats/src/test/java/org/hyperledger/besu/ethstats/EthStatsServiceTest.java:219: warning: [UnusedMethod] Method 'succeededWebSocketEvent' is never used.
    private <T> AsyncResult<T> succeededWebSocketEvent(final Optional<T> object) {

Do the tests still make sense without this?

[KYash03]

I seem to have missed that. I've removed succeededWebSocketEvent.