Add exclude-current to inputs in action

[matanbaruch]

Issue #, if available:
No specific issue referenced.

Description of changes:
This pull request introduces the exclude-current input parameter to the fast-apt-mirror.sh action. This addition allows users to exclude the currently configured APT mirror from the speed tests, enhancing flexibility and control in mirror selection.

Key changes:

1. Added exclude-current input to action.yml with a default value of false.
2. Modified the script logic to include the --exclude-current flag when this input is enabled.
3. Updated descriptions in the input section for clarity.

[sebthom]

Thanks!