docs(custom-decorators): specify getRequest type

[axel7083]

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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)
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• Other... Please describe:

What is the current behavior?

Issue Number: N/A

What is the new behavior?

Does this PR introduce a breaking change?

• Yes
• No

Other information

I was a bit lost trying to create a decorator which parse the query parameter of my request, because by default using the provided example, the request is typed as any.