Create Cryptographic Hash API in Java (Spring Boot)

Description:
Develop a RESTful API in Java using Spring Boot that exposes endpoints to compute cryptographic hashes (e.g., SHA-256, SHA-512) of user-provided text. This introduces contributors to backend development and cryptographic APIs.

Expected Tasks:

• Create a new api/ folder
• Set up a basic Spring Boot application (HashVaultApplication.java)
• Implement REST endpoints:
  • POST /hash — takes raw text and hashing algorithm as input
  • Returns computed hash (Base64 or hex format)
• Store the hash results in-memory (e.g., using a ConcurrentHashMap)
• Add basic error handling (e.g., invalid input or unsupported hash type)
• Create an API.md file with:
  • Endpoint descriptions
  • Sample requests/responses using curl or Postman
• Link this module from the root README.md

Stretch Tasks:

• Add support for hash comparison (e.g., input hash vs. new input)
• Add simple authentication (e.g., token-based or API key)