Provide a dedicated hook point for customizing InfluxDB's HTTP client

[wilkinsona]

#9669 updated InfluxDbAutoConfiguration so that it uses an optional OkHttpClient.Builder bean when creating the InfluxDBImpl instance. This feels a little to broad to me as any OkHttpClient.Builder bean will be used. I think we'd better with a mechanism that's specific to InfluxDbAutoConfiguration. That could be via a qualifier, an InfluxDbOkHttpClientBuilderProvider interface, or something else.