feat: add --insecure for login command to skip tls verify

[chlins]

This pull request introduces support for insecure connections to the registry by adding a new Insecure flag and updating the relevant code to handle this new option. The most important changes include modifications to the command-line interface, backend login logic, and configuration structure.

Command-line Interface Updates:

• Added a new --insecure flag to the login command to allow insecure connections to the registry (cmd/login.go).

Backend Login Logic:

• Imported necessary packages for handling HTTP and TLS configurations (pkg/backend/login.go).
• Updated the Login function to configure the HTTP client with the InsecureSkipVerify option based on the new Insecure flag (pkg/backend/login.go).

Configuration Structure:

• Added an Insecure boolean field to the Login struct to store the insecure connection option (pkg/config/login.go).
• Initialized the Insecure field in the NewLogin function to its default value (pkg/config/login.go).

[gaius-qi]

LGTM