feat: move caption color and font to theme.json

[HardeepAsrani]

Summary

This PR moves the Color & Typography to theme.json to avoid it overriding Site Editor preferences.

Will affect visual aspect of the product

NO

Screenshots

Test instructions

• Add an Image or Table with the caption
• Make sure the color changes if you change it to the sidebar.

Closes #56.

[pirate-bot]

Plugin build for 6fb6ca92e69c676b3d09c41d619292ed41b6583d is ready :bellhop_bell:!

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[pirate-bot]

:tada: This PR is included in version 1.1.0 :tada:

The release is available on GitHub release

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