feat(core): add RouterModule (e.g., for versioning)

[kamilmysliwiec]

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?

[ ] Bugfix
[x] 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
[x] No

Other information

[coveralls]

Pull Request Test Coverage Report for Build 97f1bc4e-4f6d-4bee-9541-5896b87221c0

• 76 of 83 (91.57%) changed or added relevant lines in 10 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.06%) to 94.68%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
packages/core/middleware/routes-mapper.ts	20	27	74.07%

Totals
Change from base Build ba2889c0-ee13-4278-a9af-fba2d8785eb1:	-0.06%
Covered Lines:	5143
Relevant Lines:	5432

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💛 - Coveralls