Bucket schema management API?

Proposal:
A BucketSchemaApi to provide convenient access to the bucket schema management features.

Current behavior:

• While it is possible to create an "explicit" Bucket through the Java API, it is not possible to create a bucket schema

Desired behavior:
I want to be able to create a bucket schema for an explicit schema bucket

Alternatives considered:
The only way to do this currently is to directly use the InfluxDb HTTP API. Its quite awkward to be able to access almost all of the InfluxDb features through the client lib, but have to drop down to using a separate HTTP lib and JSON serialization/deserialization lib for my bespoke type for representing bucket schema.

Use case:
Bucket schema seem pretty important for ensuring bucket contents will always fulfill some basic content constraints. An implicit bucket can contain anything, so would require a ton of data validation for even the simplest use-case of bucket content consumption.

Start by reviewing the existing Java bucket APIs and the proposed BucketSchemaApi, then compare them with the InfluxDB HTTP API referenced in the issue. Done means the client can create a bucket schema for an explicit-schema bucket without requiring a separate HTTP or JSON library.