Refactor environment API methods for create and update

[mawasile]

This pull request to the internal/services/environment package introduces changes to improve the validation of environment details during creation and update operations. The most important changes include renaming existing validation methods for clarity, adding new methods for update validation, and updating the corresponding data transfer objects (DTOs) and tests.

Improvements to validation methods:

• internal/services/environment/api_environment.go: Renamed ValidateEnvironmentDetails to ValidateCreateEnvironmentDetails to better reflect its purpose. [1] [2] [3]
• internal/services/environment/api_environment.go: Added a new method ValidateUpdateEnvironmentDetails for validating environment details during updates.

Updates to DTOs:

• internal/services/environment/dto.go: Renamed validateEnvironmentDetailsDto to validateCreateEnvironmentDetailsDto and added a new validateUpdateEnvironmentDetailsDto for update validation.

Test enhancements:

• internal/services/environment/resource_environment_test.go: Added a new test TestAccEnvironmentsResource_Validate_Domain_Uniqueness_On_Update to validate domain uniqueness during environment updates.