Add loading stage to various parts of the UI

[shangyian]

Summary

This PR adds a loading stage to various parts of the UI so that users know DJ is doing something when they click a button:

• Link dimensions popover
• Node validation query run

Test Plan

• [ ] PR has an associated issue: #
• [x] make check passes
• [x] make test shows 100% unit test coverage

Deployment Plan

[netlify[bot]]

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