enable wandb sync (fix datastore issues)

[raubitsj]

This PR makes wandb sync mostly work

Still a bunch of issues with wandb sync:

• [ ] hardcoded settings, need settings in wandb sync (want to clean this up in rc5)
• [ ] metadata isnt saved (need to fix the implementation to be more compatible with cling methods)
• [ ] runtime isnt right (similar to metadata we need to be saving this somewhere)
• [ ] need better datastore read tests (write path was well tested)

[coveralls]

Pull Request Test Coverage Report for Build 87c42f64-162b-48f7-9e5d-408570cd51c6

• 7 of 63 (11.11%) changed or added relevant lines in 4 files are covered.
• 3 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.1%) to 64.361%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
wandb/cli/cli.py	0	3	0.0%
wandb/internal/datastore.py	0	7	0.0%
wandb/sync/sync.py	6	52	11.54%
<!--	Total:	7	63	11.11%	-->

Files with Coverage Reduction	New Missed Lines	%
wandb/cli/cli.py	1	61.16%
wandb/sync/sync.py	2	24.04%
<!--	Total:	3		-->

Totals
Change from base Build 5e14ccb1-282f-4d45-90f4-017561485d3c:	-0.1%
Covered Lines:	12210
Relevant Lines:	18971

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💛 - Coveralls