Update pipeline email service UI text

What does this MR do?

Updates the UI Text for the pipeline email integration:

Minor copy edits for clarity, and moves the help text out of the input field.

Resolves #300614 (closed)

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Screenshots
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Does this MR meet the acceptance criteria?

Conformity

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Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
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Security

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