[Feature]: Notify about important updates

[nicholasdille]

What are you missing?

• List important tools in environment variable UNIGET_NOTIFY
• Show release notes for those tools
• Do not show other updates on the console (when env var is set)
• Option 1: Show during uniget update or uniget upgrade
• Option 2: Package release notes and add new subcommand uniget release-notes for displaying specific release notes

Requires #314 and #315

What do you expect?

No response

Have you considered alternatives?

No response

What is the context?

No response

[nicholasdille]

Migrated to https://gitlab.com/uniget-org/cli/-/issues/14