Optimizations and simplifications

[tim0n3]

Optimizations made:

• Replaced the hash command with command -v, which is more portable and POSIX compliant.
• Combined the apt update and apt install commands into a single command to reduce the number of commands executed.
• Simplified the command to retrieve the system's IP address by using the ip -4 addr show command and filtering the output with grep and awk.
• Removed the redundant grep command in the condition for checking the number of IPv4 addresses on the system.
• Simplified the command for selecting the user's desired IPv4 address by using sed instead of grep and cut.
• Use a case statement instead of multiple if/elif statements when detecting the OS for better code readability.
• Use a function + case statement to print the error messages and exit when a required OS version is not met.

I've taken liberties with the format as I haven't look at your code guidelines/requirements for PRs but hope you'll consider this one.

[Nyr]

• I do not remember specifics now, but there is a reason to use hash instead of command in that context.
• The apt change does not reduce the number of commands executed. And why use apt instead of apt-get in a script like this?
• It makes no sense to "simplify" already robust and tested approaches which have been used over the years. For example, your commit introduces the use of awk. While being a powerful tool, I intentionally avoided dependance on awk (and other commands) as it is not present in every system. Your pull request breaks the script in every system where awk is not present.