feat(logs): Log duplicate handlers

[ZimGil]

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
• 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?

Currently duplicate handlers override each other with the last one taking place.
This can be confusing and hard to find in large scale applications.

Issue Number: N/A

What is the new behavior?

Added warning level logs to indicate these cases

Does this PR introduce a breaking change?

• Yes
• No

Other information