Improve imports

[bryanlopezinc]

PR Summary

• Validate input options when importing items from the CLI.
• Validate the import type to prevent errors when an invalid type is provided, applicable to both CLI and API endpoints.
• Fixed an issue in the import command where a success message was returned even when the import file did not exist.
• Remove the deprecated method fetchOne

Checklist:

• I have read the Contributing documentation available here: https://snipe-it.readme.io/docs/contributing-overview
• I have formatted this PR according to the project guidelines: https://snipe-it.readme.io/docs/contributing-overview#pull-request-guidelines
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[what-the-diff]

PR Summary

• Improved Import Command Functionality

  • The object import command has been refined. We added a mechanism that checks the validity of an import file to make sure it exists and follows the rules we set. This helps in avoiding faulty operations.
  • We've made it easier to create importers and included more detailed error messages if something goes wrong during the import.

• New Factory Class

  • A new class called 'Factory' has been created. This is responsible for creating appropriate importer objects based on what type of item we're importing. So it's a smart way to keep our import operations flexible and manageable.

• Constant Class for Mime Types

  • A new class accommodating supported types of import files has been created. It ensures we work with valid file types and helps avoid errors.

• Defined Type of Importers

  • We have introduced a way to define valid types of importers and a function to obtain these types, making it easier for future command-line operations.

• Improved Request Validation

  • The rules validating the types of items being imported have been improved. This ensures we only deal with valid items.

• Upgraded Importer Class

  • Changes were made to the import method making it easier to recognize the header row, improving the efficiency of the import operation.

• Added Tests

  • New tests were created to make sure our import command works well, which includes a variety of scenarios and checks. This will make it easier for us to catch any potential issues early on.

• Code Cleanup

  • Some minor changes were made to improve the style of the code and the clarity of the comments.

[snipe]

Hiya - looks like there's a merge conflict here - can you take a look?