fix: wrong base url for staging env

[RMCampos]

This pull request includes several updates related to environment configuration, logging improvements, and dependency upgrades. The main focus is on improving the handling of environment-specific URLs, increasing logging visibility for email-related actions, and updating the Spring Boot version.

Environment configuration and URL handling:

• Updated the logic in MailgunEmailService#getBaseUrl to correctly construct the base URL for the "staging" environment, ensuring that the domain is adjusted for staging deployments.
• Changed the TARGET_ENV variable in the terraform-stg/main.tf Kubernetes deployment from "production" to "staging", aligning the infrastructure configuration with the intended environment.

Logging improvements:

• Added logging statements in MailgunEmailService to output the generated confirmation and password reset links, aiding in debugging and monitoring email operations. [1] [2]
• Updated the logger initialization in MailgunEmailService to use the class name string, ensuring consistency and clarity in log outputs.

Dependency updates:

• Upgraded the Spring Boot version from 4.0.3 to 4.0.5 in server/pom.xml to incorporate the latest fixes and improvements.