Add Comet support in experiment create

[mjlangan]

Most of the changes are copy/pasting the API files from beaker-service into this repository.

Sample output from creating an experiment with Comet enabled:

$ ./beaker experiment create -f ~/Desktop/beaker_experiments/basic_comet_exp.yaml 
Experiment ex_61bb3ge7fqgg submitted. See progress at http://localhost:9027/ex/ex_61bb3ge7fqgg
Comet.ML experiments were created for each task in this experiment.
tk_j9j1jz4qsokd: https://staging.comet.ml/michaell/general/beaker5557f3b0e7b14c6a959e340c16a281d8
tk_ztlyl97a8las: https://staging.comet.ml/michaell/general/beaker847f7098788a473385814458678f366a
tk_qmtj1p48ftl4: https://staging.comet.ml/michaell/general/beakerdeed02df74494ba59e7db9dea0c61807