Add synapse/lib/drive.py for versioned hierarchical storage object and plumb in Cell

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 99.75610% with 1 line in your changes missing coverage. Please review.

Project coverage is 96.30%. Comparing base (d8a6a2e) to head (7f6a38a). Report is 2 commits behind head on master.

Files	Patch %	Lines
synapse/lib/cell.py	98.43%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #3856 +/- ## ========================================== - Coverage 96.35% 96.30% -0.06% ========================================== Files 243 244 +1 Lines 54059 54469 +410 ========================================== + Hits 52088 52454 +366 - Misses 1971 2015 +44 ``` | [Flag](https://app.codecov.io/gh/vertexproject/synapse/pull/3856/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vertexproject) | Coverage Δ | | |---|---|---| | [linux](https://app.codecov.io/gh/vertexproject/synapse/pull/3856/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vertexproject) | `96.30% <99.75%> (+0.02%)` | :arrow_up: | | [linux_replay](https://app.codecov.io/gh/vertexproject/synapse/pull/3856/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vertexproject) | `?` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vertexproject#carryforward-flags-in-the-pull-request-comment) to find out more.

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[invisig0th]

Does this need a changelog entry or is it internal enough we can skip one for now?

I was thinking this was "internal" and we should skip a changelog entry :+1: