refactor: Add debug mode and refactor print_notifs

[LangLangBart]

description

• Add an environment variable to enable more debug information. This is useful when identifying the
  cause of an issue, e.g., Notifications for releases are not listed #83 by @rEnr3n.

# For example, the file will catch all stdout and stderr, as well as everything from 'xtrace'
GH_NOTIFY_DEBUG_MODE='true' gh notify -an 20
[DEBUG] /Users/paria/.local/share/gh/extensions/gh-notify/gh_notify_debug.log

• Split the 'print_notifs' into smaller functions for readability.

• Fix retrieval for notifications with more than 50 items requested; previously, it would just
  ignore them and deliver only 50.

• Prepend command to all command calls

# Execute the `cat` command, even if an `cat` alias exists:
command cat

• Check if bat or batcat is installed for diffs on PR's

• Clarify user facing texts