[v2] Capture stack outputs

[blampe]

This returns stack outputs from the agent and records them in a secret.

• OutputValue is returned from the agent and contains raw JSON-encoded bytes for the output.
• Each Update owns a corresponding -stack-outputs secret.
• The secret includes a pulumi.com/secrets annotation with a list of sensitive fields, and the Stack API uses this to scrub outputs for the Stack's status.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 62.04380% with 52 lines in your changes missing coverage. Please review.

Project coverage is 49.11%. Comparing base (8ac74b0) to head (7f11ec4). Report is 1 commits behind head on v2.

Files with missing lines	Patch %	Lines
...ator/internal/controller/auto/update_controller.go	65.11%	24 Missing and 6 partials :warning:
agent/pkg/server/server.go	38.09%	11 Missing and 2 partials :warning:
...tor/internal/controller/pulumi/stack_controller.go	70.83%	4 Missing and 3 partials :warning:
...r/internal/controller/auto/workspace_controller.go	66.66%	1 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## v2 #676 +/- ## ========================================== + Coverage 47.27% 49.11% +1.83% ========================================== Files 26 26 Lines 2807 2877 +70 ========================================== + Hits 1327 1413 +86 + Misses 1316 1287 -29 - Partials 164 177 +13 ```

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