docs(operators): add JSDoc for `mapResponse`

[rainerhahnekamp]

PR Checklist

Adds JSDoc for mapResponse

Please check if your PR fulfills the following requirements:

• [ ] The commit message follows our guidelines: https://github.com/ngrx/platform/blob/main/CONTRIBUTING.md#commit
• [ ] Tests for the changes have been added (for bug fixes / features)
• [x] Documentation has been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[x] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

Closes #4336

Does this PR introduce a breaking change?

[ ] Yes
[x] No

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