docs: fix AOT instructions for global custom http parameter codec

[mokipedia]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[X] 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?

Current example in docs will not work with AOT: function call in decorator is not allowed

Issue Number: N/A

What is the new behavior?

using a object literal to circumvent constructor call

Does this PR introduce a breaking change?

[ ] Yes
[X] No

Other information

[mokipedia]

that approach also leads to problems, so closing this until a better solution is found