feat: add user-defined config for syntax highlighting plugin (#869)

* feat: add user-defined options to syntax highlighting plugin

* feat: add default syntax highlighting config to `quartz.config.ts`

* chore: refactor according to @aarnphm's review

Co-authored-by: Aaron Pham <29749331+aarnphm@users.noreply.github.com>

* chore: run Prettier on `quartz/plugins/transformers/syntax.ts`

* Update quartz/plugins/transformers/syntax.ts

Co-authored-by: Jacky Zhao <j.zhao2k19@gmail.com>

* Update syntax.ts

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Co-authored-by: Aaron Pham <29749331+aarnphm@users.noreply.github.com>
Co-authored-by: Jacky Zhao <j.zhao2k19@gmail.com>