Add copilot auto login through env vars

[TheGupta2012]

Authentication and Token Management:

• Added the get_gh_access_token_from_env() function in lab_notebook_intelligence/github_copilot.py to retrieve and decrypt the GitHub access token from the NBI_GH_ACCESS_TOKEN_ENCRYPTED environment variable, using a password from NBI_GH_ACCESS_TOKEN_PASSWORD or a default value.
• Updated login_with_existing_credentials() to prioritize the environment variable token and avoid storing it if present.
• Modified token retrieval logic in get_token() and get_token_thread_func() to use the environment variable token if available, falling back to the stored token otherwise. [1] [2]

Inline Completion Logic Update

• Only trigger inline completions if the user input changes from the current completion