feat: detect eslint flat and eslintrc configs

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What does this MR do and why?

Add support for detecting eslint flat configs (v9), such that the default config will not be written when either an eslint flat config or an eslintrc config is present.

Fix bug where if there are multiple eslintrc config files matching the .eslintrc.* pattern bash will error out (https://gitlab.com/gitlab-community/components/code-quality-oss/javascript-codequality/-/jobs/10202728191):

/usr/bin/bash: line 162: [: .eslintrc.js: binary operator expected

Closes #27 (closed)

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Screenshots or screen recordings

Current state before this change: https://gitlab.com/gitlab-community/components/code-quality-oss/javascript-codequality/-/jobs/10202477001

Example of an eslint flat config being used: https://gitlab.com/gitlab-community/components/code-quality-oss/javascript-codequality/-/jobs/10202601548

Example of an eslintrc config being used: https://gitlab.com/gitlab-community/components/code-quality-oss/javascript-codequality/-/jobs/10202631230

Example of multiple eslintrc config not producing bash errors: https://gitlab.com/gitlab-community/components/code-quality-oss/javascript-codequality/-/jobs/10202731605

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