Fix docs deployment

[chatton]

Description

This PR syncs the Makefile target with the one in the cosmos-sdk repo, removes additional uneeded dependencies, and adds the option to trigger a docs deployment through the UI (via workflow_dispatch)

The docs built from this PR are live here 🥳

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Before we can merge this PR, please make sure that all the following items have been
checked off. If any of the checklist items are not applicable, please leave them but
write a little note why.

• Targeted PR against correct branch (see CONTRIBUTING.md)
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the module structure standards.
• Wrote unit and integration tests
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added relevant godoc comments.
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer
• Review Codecov Report in the comment section below once CI passes

[colin-axner]

Aye! Marvelous!! 💛

[damiannolan]

Nice job!