no-dotenv: add "allowFileNames" option

[azu]

@secretlint/secretlint-rule-no-dotenv is file name based rule.

We want to provide that the user can ignore specific files like .env.local.
Of course, .secretlintignore allows us to define it. However, it should be the rule's option too.

📝 If we will create more file name-based rules like https://github.com/eth0izzle/shhgit/blob/master/config.yaml, we need to get versatile approach.