new: Improve generated command help page formatting using Rich

[lgarber-akamai]

📝 Description

This change makes various large formatting improvements to command help pages, including:

• Bolding help page sections
• Adding color/bolding to argument names and prefixes
• Grouping arguments by parent and whether they are required
• Applying indentation to child arguments
• Converting Markdown links to human-readable absolute links

Additionally, this PR moves help page helpers from arg_helpers.py to a new help_pages.py file in an effort to keep files tightly scoped

✔️ How to Test

The following test steps assume you have pulled this code locally and run make install.

Unit Testing

make testunit

Integration Testing

make testint

Manual Testing

1. View the help page for any CLI command (e.g. linode-cli linodes ls --help).
2. Ensure the output matches the criteria mentioned in the description and is readable/understandable.

📷 Preview

linodes ls	linodes create

firewalls update	firewalls delete