Docs on manually triggering builds and previews

[ethanpalm]

Documentation changes

This PR documents how to manually build your docs site and how to manually create a preview.

I added an article on deployments so that there is room to grow that topic with future content and this isn't appropriate for the quickstart. Open to opinions on the placement of the deployment content though.

Closes https://linear.app/mintlify/issue/DOC-45/how-to-retrigger-a-build

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