feat(env): deprecate glab variables without GLAB_ prefix

Description

Environment variables used by glab are going to be prefixed with GLAB_, namely:

• GLAMOUR_STYLE
• DEBUG
• NO_PROMPT
• FORCE_HYPERLINKS

Environment variables that will continue working as before are:

• BROWSER - the process spawned by the command to start the browser inherits the environment variables, so it doesn't make sense to have GLAB_BROWSER to rename it to BROWSER
• NO_COLOR - the tool follows the https://no-color.org/ specification
• VISUAL - considered one of the default values nowadays
• EDITOR - considered one of the default values nowadays

• minor(env): deprecate glab variables without GLAB_ prefix

Related Issues

Resolves #7965 (closed)

How has this been tested?

❯ GLAB_NO_PROMPT=true ./bin/glab mr create
ERROR: --title or --fill required for non-interactive mode.
Try 'glab mr create --help' for more information.

❯ NO_PROMPT=true ./bin/glab mr create
DEPRECATION WARNING: The environment variable NO_PROMPT has been deprecated and will be removed in future releases. Use GLAB_NO_PROMPT instead.
ERROR: --title or --fill required for non-interactive mode.
Try 'glab mr create --help' for more information.

❯ GLAMOUR_STYLE=light ./bin/glab issue view 7928 | head -3
DEPRECATION WARNING: The environment variable GLAMOUR_STYLE has been deprecated and will be removed in future releases. Use GLAB_GLAMOUR_STYLE instead.
title:	glab release fails with 422 when using --publish-to-catalog
state:	open

❯ GLAB_GLAMOUR_STYLE=light ./bin/glab issue view 7928 | head -3
title:	glab release fails with 422 when using --publish-to-catalog
state:	open
author:	ignacio.piqueras

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation
• Chore (Related to CI or Packaging to platforms)
• Test gap