Better handle missing files

[verovaleros]

Description

Fixes #30

This PR introduces checks to validate the following files exists:

• honeypots_public_ips.csv: this file must exist, now raising an error if it's missing.
• do_not_block_these_ips.csv: this file can or cannot exist, now continuing with an empty data frame.

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• Tested with both files missing
• Tested with honeypot public ips missing and do not block these ips present
• Tested with do not block these ips missing and honeypot public ips present
• Tested with both files present

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings