Allow users to customize variables in tailwindcss

[spikelu2016]

Describe the solution you'd like Users should be able to define customized global variables in tailwindcss config file for Bricks to automatically detect and use it in our code

[donfour]

Possibly related to https://github.com/bricks-cloud/bricks/issues/76 and https://github.com/bricks-cloud/bricks/issues/77.

If the Figma design has text styles and fill styles set up, we can automatically create tailwind config with global variables.