Non-interactive mode for --shell and integration changes

[TheR1D]

• Added --interaction that works with --shell option, e.g. sgpt --shell --no-interaction will output suggested command to stdout without asking user for any input.
• Changed shell integrations to use new --no-interaction option to get suggested shell command output from sgpt.
• Moved shell integrations into dedicated file integration.py.
• Changed --install-integration logic so sgpt can install integrations without downloading sh scripts.
• Removed validation for PROMPT argument, now will be empty string by default.
• Fixing an issue when sgpt is being called from non-interactive shell environments such us cron tab.
• Fixed and optimised Dockerfile.
• README.md improvements, and new feature examples.