Implement metrics command (google/clasp#353)

[kalmi]

Fixes #353. CI breakage is expected due to scopes change.

Only basic metrics listing is implemented from the data provided by the getMetrics API.

Example:

$ clasp metrics
UTC Dates
2020-03-20  0 users   0 executions  0 failed
2020-03-19  0 users   0 executions  0 failed
2020-03-18  0 users   0 executions  0 failed
2020-03-17  0 users   0 executions  0 failed
2020-03-16  0 users   0 executions  0 failed
2020-03-15  1 user    1 execution   0 failed
2020-03-14  2 users  21 executions  2 failed

• [X] npm run test succeeds.
• [X] npm run lint succeeds.
• [X] Appropriate changes to README are included in PR.

A separate issue could be opened for extending the metrics command with data provided by the processes API. There is a lot of potential in the processes API for extending this command.

[PopGoesTheWza]

@kalmi can you give a look at the failing test? TIA

[kalmi]

I think the token used by the CI needs to be recreated with the new scopes. I think it comes from the CREDS env variable.

[PopGoesTheWza]

@kalmi sorry for the late reply, I no longer use clasp and rarely check this repo. If this PR is still relevant, can you give a shot at resolving the above conflicts?