[v2] Set config all at once

[blampe]

We currently issue one SetAllConfig RPC for each user-specified config. This is slow but it has important correctness guarantees:

1. The order we apply config matters -- if the user specifies foo: foo followed by foo: bar, the net result must always be foo: bar.
2. The Pulumi CLI (and therefore Automation API) only allows specifying --path on an all-or-nothing basis. This is bad for us because we potentially have a blend of path and non-path keys.

Ideally we would be able to supply all of our configs to the automation API in a single call, and in the case where all of our config keys are path-like (or all are not path-like) we actually can do that because we no longer have limitation (2).

This PR makes that possible in the general case by transforming our config keys in a way that allows us to treat them as if they are all path-like.

In particular:

• The agent's SetAllConfig handler is modified to take a list of configs instead of a map in order to preserve config order. The top-level path param is also removed and handled on a per-key basis.
• While resolving configs, we escape any non-path keys so subsequent path parsing treats them as verbatim. For example foo.bar gets escaped as ["foo.bar"].
• We can then supply all of our keys at once to Automation API with Path: true.
• If there are no configs to set then the operator doesn't invoke SetAllConfig.

Fixes #650

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 22 lines in your changes missing coverage. Please review.

Project coverage is 53.10%. Comparing base (7883699) to head (6647054).
Report is 3 commits behind head on v2.

Files with missing lines	Patch %	Lines
agent/pkg/server/server.go	73.33%	4 Missing and 4 partials ⚠️
operator/internal/controller/auto/utils.go	0.00%	7 Missing ⚠️
...r/internal/controller/auto/workspace_controller.go	0.00%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##               v2     #718      +/-   ##
==========================================
+ Coverage   53.00%   53.10%   +0.09%     
==========================================
  Files          29       29              
  Lines        3081     3096      +15     
==========================================
+ Hits         1633     1644      +11     
- Misses       1267     1269       +2     
- Partials      181      183       +2     

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[blampe]

Confirmed config still propagates as expected. Of course the StacK API is currently just a map with no path information, so all of the path optimizations are only relevant for the Workspace API. However it does give users the ability -- although somewhat clunky -- to specify somewhat structured (path: true) config via the workspaceTemplate.