docs: add HttpClientModule import code to services tutorial

[Ana06]

To be able to copy and paste, lazy people will thank it 😉

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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
[ ] angular.io application / infrastructure changes
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[mary-poppins]

You can preview 98275ee at https://pr24854-98275ee.ngbuilds.io/.
You can preview e0bb03d at https://pr24854-e0bb03d.ngbuilds.io/.
You can preview d375c2e at https://pr24854-d375c2e.ngbuilds.io/.

[brandonroberts]

@Ana06 if you're still interested in landing this PR, you'll need to sign the CLA and amend the commit message to be docs: add HttpClientModule import code to services tutorial

[googlebot]

CLAs look good, thanks!

[Ana06]

@brandonroberts done!

[mary-poppins]

You can preview 41b6616 at https://pr24854-41b6616.ngbuilds.io/.

[mary-poppins]

You can preview 57b5653 at https://pr24854-57b5653.ngbuilds.io/.

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