[FEATURE] Add support for overriding default Direct TCP options

[David-Noble-at-work]

When this issue is resolved you will be able to set Direct TCP options. In priority order we will take default Direct TCP options from:

1. The string value of system property azure.cosmos.directTcp.defaultOptions. Example:

   -Dazure.cosmos.directTcp.defaultOptions={\"maxChannelsPerEndpoint\":5,\"maxRequestsPerChannel\":30}

2. The contents of the file located by system property azure.cosmos.directTcp.defaultOptionsFile. Example:

   -Dazure.cosmos.directTcp.defaultOptionsFile=/path/to/default/options/file

3. The contents of the resource file named azure.cosmos.directTcp.defaultOptions.json. Specifically, the resource file is read from this stream:

   RntbdTransportClient.class.getClassLoader().getResourceAsStream("azure.cosmos.directTcp.defaultOptions.json")

   Example: Contents of resource file azure.cosmos.directTcp.defaultOptions.json.

   
   {
    "bufferPageSize": 8192,
    "connectionTimeout": "PT1M",
    "idleChannelTimeout": "PT0S",
    "idleEndpointTimeout": "PT1M10S",
    "maxBufferCapacity": 8388608,
    "maxChannelsPerEndpoint": 10,
    "maxRequestsPerChannel": 30,
    "receiveHangDetectionTime": "PT1M5S",
    "requestExpiryInterval": "PT5S",
    "requestTimeout": "PT1M",
    "requestTimerResolution": "PT0.5S",
    "sendHangDetectionTime": "PT10S",
    "shutdownTimeout": "PT15S"
   }

4. Otherwise, if none of these values are set or all set values are in error we will create default options based on a set of hard-wired values defined in the default private parameterless constructor for RntbdTransportClient.Options.

[David-Noble-at-work]

Work completed. See PR#308.