docs: add RulesCustomization section and fix lint.customization type (#252)

* feat: add `oxc.lint.rulesCustomization`

* improve object structure

* update tests

* default null

* Initial plan

* docs: add RulesCustomization section and fix lint.customization type in README

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* fmt: apply oxfmt formatting to README.md

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* fmt: apply oxfmt formatting to whole project

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Signed-off-by: Alexander S. <sysix@sysix-coding.de>
Co-authored-by: Sysix <sysix@sysix-coding.de>
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