Update the use of allowlist and add ignorelist for gitleaks.toml files

[gregorysprenger]

Is your feature request related to a problem? Please describe.
Currently, the use of the [allowlist] table is used to ignore file paths and regexes. I have overlooked this several times as I consider allowlist = only allow these files should be checked.

Describe the solution you'd like
Update [allowlist] to be as the name suggests - only files/regexes listed in this table should be checked. Also, implement an [ignorelist] table, where any path/regex is ignored.

cc @zricethezav

[nunofranciscomoreira]

What you're describing doesn't align with the concept of an allow list. An allow list, as the name implies, grants permission for certain actions or items. In this scenario, it permits the existence of secrets either within specified paths or those that match certain regex patterns.

It appears that what you're seeking is more akin to defining a scope rather than implementing an allow list. This distinction suggests it's a specific requirement tailored to your needs rather than a fundamental function of the tool.