Refactor(nginx): migrate to unified folder structure

[v-xuto]

This PR migrates the nginx specification to the new unified folder structure according to Azure folder structure guidelines.

Change:

• Consolidated TypeSpec and Swagger files under resource-manager\Nginx.NginxPlus\ginxPlus
• Updated tspconfig.yaml with correct paths and ARM types directory
• Fixed all common-types references and input-file paths in readme.md
• Verified TypeSpec compilation works correctly
• Updated the relevant paths in specification/suppressions.yaml file
• Updated the relevant paths in cspell.yaml file
• Add rpaas readme.md under resource-manger

Benefits:

• Unified structure for better maintainability
• Aligns with Azure folder structure standards
• Maintains backward compatibility
• Supports future TypeSpec migration efforts

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Comment generated by summarize-checks workflow run.

[github-actions]

API Change Check

APIView identified API level changes in this PR and created the following API reviews

Language	API Review for Package
Swagger	Nginx.NginxPlus-Nginx
TypeSpec	Nginx.NginxPlus

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Comment generated by After APIView workflow run.

[github-actions]

API Change Check

APIView identified API level changes in this PR and created the following API reviews

Language	API Review for Package
TypeSpec	Nginx.NginxPlus
Python	azure-mgmt-nginx
Swagger	Nginx.NginxPlus-NginxPlus

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Comment generated by After APIView workflow run.

[qiaozha]

The service name should be NginxPlus

[v-xuto]

The service name should be NginxPlus

Updated.