chore(gatsby): Update websocket-manager to TS

[Eyas]

Description

This PR migrates packages/gatsby/src/utils/websocket-manager to TypeScript.

Related Issues

Part of #21995.

[blainekasten]

This looks great to me, let's merge it!

Thank you so much for contributing to our TypeScript refactor! We have more work to do and we would love to have you stay involved in our transition. Please submit more PRs! 💜

[gatsbot]

Holy buckets, @Eyas — we just merged your PR to Gatsby! 💪💜

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