[terra-aggregator] Mark terra-aggregator for deprecation.

[mjhenkes]

Feature Request

Description

Update the terra-aggregator package to indicate that it will be deprecated in the future.
Update terra-aggregator documentation to indicate that it will be deprecated in the future using the deprecation notice.

This component will be supported by terra until a broad terra change that would require a major version. (e.g. React 17).

terra-aggregator was created specifically for the needs of a single team, uses beyond that team were not considered at the time and this is not a component we wish to support broadly. Our recommendation for teams that use this component is to fork the component and takeover maintenance.

Per audit #1231

Additional Context / Screenshots

@ Mentions

[mjhenkes]

Let's make sure we hold on this one. We need to re-evaluate usage.

[stale]

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