unify blockquote introduction for the components
minor #3906 Blockquote introductions (xabbuh)

This PR was merged into the 2.3 branch.

Discussion
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Blockquote introductions

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets |

Most component descriptions start with a blockquote introducing the purpose of a particular component. This pull requests adds these introductions where they are missing.

Commits
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6d7ef9c unify blockquote introduction for the components