feat!: switch the recommended config to flat

[aladdin-add]

This PR adds support for the new eslint config, an example:

// eslint.config.js
const pluginSecurity = require('eslint-plugin-security');

module.exports = [pluginSecurity.configs.recommended];

[nzakas]

Thanks, just one question.

Also, it would be helpful to include a description of the pull request. "Support eslint.config.js" doesn't adequately explain the changes you made here.

[aladdin-add]

@nzakas I've updated the title and description to be clearer. can you take another look?

notes: not sure why the pr checker does not know feat!.

[nzakas]

LGTM. Thanks!

[nzakas]

Yeah, looks like it doesn't support that format. I don't have time to look into that right now, but if you do, please feel free.