Update task run status with results

[othomann]

Changes

Corresponding changes to update the task run status with the new results from the task spec.

Submitter Checklist

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review them:

• Includes tests (if functionality changed/added)
• Includes docs (if user facing)
• Commit messages follow commit message best practices

Reviewer Notes

If API changes are included, additive changes must be approved by at least two OWNERS and backwards incompatible changes must be approved by more than 50% of the OWNERS, and they must first be added in a backwards compatible way.

Release Notes

Provide the task run status update to reflect the new results defined in the task spec.

[ghost]

The code looks great.

Now that this feature is more fully supported I suggest we add info to the user-facing docs:

1. docs/tasks.md should include a Syntax sub-section called "Results". This section should include the following:

   1. a description of "results"' purpose. Something short like "Results allow a Task to output string data" is fine for now because that data can't be used in subsequent tasks yet.
   2. A description of the file path that a task should write to output a result.
   3. A short spec yaml showing usage (similar to the one you included here).

2. docs/taskruns.md should include a sub-section under "Status" that describes the format of the results written out to the TaskRun.

3. Add an example under examples/taskruns that utilizes results. This example will act as documentation (we should link to it from docs/tasks.md) and will also act as an end-to-end test since our examples are executed on a running cluster with each PR.

[ghost]

/approve

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[othomann]

@sbwsg you want the doc changes as part of this PR?

[ghost]

yes please!

[ghost]

/lgtm