feat(client): support namespace and requester (#217)

Because

- improve DX of client usage and endpoint functions

This commit

- unify client initialization interface
- support client level `requester`
- support endpoint level target `namespace`
- remove configuration system

resolves INS-6456
resolves INS-6457
resolves INS-6458

Author: heiruwu

instill/__main__.py

@@ -1,11 +1,6 @@
 #!/usr/bin/env python
 
 """Package entry point."""
-import pprint
-
-from instill.configuration import global_config
 
 if __name__ == "__main__":  # pragma: no cover
-    # main()  # pylint: disable=no-value-for-parameter
-    print("======================Configured Hosts======================")
-    pprint.pprint(global_config.hosts)
+    pass  # pylint: disable=no-value-for-parameter

instill/clients/__init__.py

@@ -1,4 +1,4 @@
-from instill.clients.client import InstillClient, get_client
+from instill.clients.client import InstillClient, init_core_client
 from instill.clients.mgmt import MgmtClient
 from instill.clients.model import ModelClient
 from instill.clients.pipeline import PipelineClient