[client-v2] Prevent using http client before it is initialized

[chernser]

Describe the bug

Apache HTTP Client is used internally to make http calls. It take a time to initialize it but application may start doing requests.
It will cause internal exception and exception is not recoverable.

Steps to reproduce

1. Create client
2. Immediately send some request

Expected behavior

Request is executed successfully

Error log

com.clickhouse.client.api.ClientException: Failed to execute request
	at com.clickhouse.client.api.internal.HttpAPIClientHelper.executeRequest(HttpAPIClientHelper.java:385)
	at com.clickhouse.client.api.Client.lambda$insert$7(Client.java:1393)
	at com.clickhouse.client.api.Client.runAsyncOperation(Client.java:1942)
	at com.clickhouse.client.api.Client.insert(Client.java:1485)
	at 
...
Caused by: java.lang.IllegalStateException: Connection pool shut down
	at org.apache.hc.core5.util.Asserts.check(Asserts.java:38)
	at org.apache.hc.core5.pool.LaxConnPool.lease(LaxConnPool.java:163)
	at org.apache.hc.client5.http.impl.io.PoolingHttpClientConnectionManager.lease(PoolingHttpClientConnectionManager.java:298)
	at org.apache.hc.client5.http.impl.classic.InternalExecRuntime.acquireEndpoint(InternalExecRuntime.java:103)
	at org.apache.hc.client5.http.impl.classic.ConnectExec.execute(ConnectExec.java:125)
	at org.apache.hc.client5.http.impl.classic.ExecChainElement.execute(ExecChainElement.java:51)
	at org.apache.hc.client5.http.impl.classic.ProtocolExec.execute(ProtocolExec.java:192)
	at org.apache.hc.client5.http.impl.classic.ExecChainElement.execute(ExecChainElement.java:51)
	at org.apache.hc.client5.http.impl.classic.HttpRequestRetryExec.execute(HttpRequestRetryExec.java:96)
	at org.apache.hc.client5.http.impl.classic.ExecChainElement.execute(ExecChainElement.java:51)

Configuration

Environment

• Client version: 0.7.1