fix: Make `tailwindcss` peer dependency optional

[amannn]

fix: Make tailwindcss peer dependency optional

Description

This makes this plugin easier to consume when it's installed as part of a shared config, in case tailwindcss is not installed by the host.

See also: https://github.com/jest-community/eslint-plugin-jest/pull/970

Type of change

• [x] Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Known to work from other plugins.

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• [x] Any dependent changes have been merged and published in downstream modules
• [x] I have checked my code and corrected any misspellings