feat(common): add UNPROCESSABLE_CONTENT for status 422

[shivamgupta29]

Adds the HttpStatus.UNPROCESSABLE_CONTENT enum in alignment with RFC 9110. The previous HttpStatus.UNPROCESSABLE_ENTITY is now marked as deprecated.

PR Checklist

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• 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?

The framework currently only provides HttpStatus.UNPROCESSABLE_ENTITY for the 422 status code. This name is based on the obsolete RFC 4918.

Closes #15624

What is the new behavior?

This PR introduces HttpStatus.UNPROCESSABLE_CONTENT for the 422 status code, aligning the framework with the current RFC 9110 standard. The previous enum, HttpStatus.UNPROCESSABLE_ENTITY, has been marked as @deprecated to maintain backward compatibility while guiding users to the correct, modern standard.

Does this PR introduce a breaking change?

• Yes
• No

[coveralls]

Pull Request Test Coverage Report for Build e477f746-46bc-447a-9c99-453ca022d9d4

Details

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.002%) to 88.736%

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Totals
Change from base Build 87823697-4182-4d9a-8625-1cc37cfa7f74:	0.002%
Covered Lines:	7271
Relevant Lines:	8194

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💛 - Coveralls