chore(core): allow dynamic value for header value

[dammy001]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• 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?
closes #13012

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• 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

[coveralls]

Pull Request Test Coverage Report for Build 7c9477ff-a808-444d-84b1-9d6b0d470d13

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 92.1%

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Totals
Change from base Build 30e0c3c6-7ddd-4f52-807f-f3506861f267:	0.0%
Covered Lines:	6715
Relevant Lines:	7291

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💛 - Coveralls

[micalevisk]

I guess we should clarify in the docs for this feature when exactly the function will be invoked

[kamilmysliwiec]

We'd need to update this decorator signature too https://github.com/nestjs/nest/blob/master/packages/common/decorators/http/header.decorator.ts#L17

[dammy001]

We'd need to update this decorator signature too https://github.com/nestjs/nest/blob/master/packages/common/decorators/http/header.decorator.ts#L17

Updated. Thanks @kamilmysliwiec