Support custom host name for SegmentIntegration

[prayansh]

In our efforts to support data residency, these changes allow our SDK to retrieve a custom apiHost name from settings and also provides a new builder option to provide a defaultApiHost().

The host name can be configured via app.segment.com under the individual source's settings.
If the SDK were to fail while fetching settings from the internet, we use the defaultApiHost property for configuration

Usage

Analytics.Builder(this, ANALYTICS_WRITE_KEY)
             .defaultApiHost("api.segment.io/v1")