Incorrect URLs formed if base URL contains a path segment

(Tested with influxdb-java version 2.5)

We're using a HTTPS reverse proxy in front our influxdb instance.

The external URLs is `https://scala-ci.typesafe.com/influx/write`.

The URL actually generated by influxdb-java is `https://scala-ci.typesafe.com/write`.

I believe that changing `@POST("/write")` to `@POST("write")`, etc, in `InfluxDBService.java` would fix this, but haven't verified.

A workaround is to add an interceptor to fixup the URL.

```java
OkHttpClient.Builder client = new OkHttpClient.Builder();
client.addNetworkInterceptor(chain -> {
HttpUrl.Builder fixedUrl = chain.request().url().newBuilder().encodedPath("/influx/" + chain.request().url().encodedPath().replaceFirst("/influxdb", ""));
return chain.proceed(chain.request().newBuilder().url(fixedUrl.build()).build());
});
InfluxDB influxDB = InfluxDBFactory.connect("https://scala-ci.typesafe.com/influx/", user, password, client);
```

Inizia leggendo InfluxDBService.java e seguendo come le sue annotazioni dell’endpoint si combinano con un URL di base contenente /influx. Riproduci la richiesta segnalata verso https://scala-ci.typesafe.com/influx/ e verifica che gli URL generati conservino il segmento del percorso di base senza richiedere il workaround dell’interceptor.

Scritto dal modello di indicizzazione a partire dal testo della issue.