19895: Upgrade google-api-python-client

19895: Upgrade google-api-python-client

Version 2.0 tries to load all discovery documents from a local cache. It
added a new argument to discovery.build(static_discovery=False) to
retrieve the discovery document from the network.

Version 2.1 improves backwards compatibility by having static_discovery
default to False when you pass an explicit discoveryServiceUrl to
discovery.build(). We always do this (see
arvados.api.normalize_api_kwargs), so we can upgrade to version 2.1
without making any changes to our own SDK.

Doing so is just good hygiene, and makes life easier for users who want
to build projects that use both Google services and Arvados.

Version 2.1 was released on 2021-03-31, so this new version requirement
should be easy enough for most users to satisfy.

Arvados-DCO-1.1-Signed-off-by: Brett Smith <brett.smith@curii.com>