Add feature flag support

[JinnyYi]

We use go-integration-test to execute integration tests on services. And all services should add integration tests for operations declared in service.toml.

Excepted Behavior

All services should pass integration tests for operations declared in service.toml, including the basic interface tests, uniformized behavior and some characteristics.

Current Behavior

For some features or behavior, not all services are supported. When we make these behaviors mandatory test cases, there are problems with some integration test cases not passing. And non-stop split tests will lead to too much content to test and complex test cases.

Possible Solution

Add feature flag support:

• Services should declare supported features.
• go-integration-test run the tests cases according to the features.

Related Issues

• Linear Issue: go-storage Add feature flag support
• one-drive conflict with the design of the empty file

[Xuanwo]

This issue will also fix #756 (comment)