feat: add pscale completion spec

[gusfune]

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

Adds PlanetScale CLI specs as requested on #661. (Closes #661)

[withfig-bot]

Overview

src/pscale.ts:

Info:

URLs:

• https://api.planetscale.com/

[withfig-bot]

Hello @gusfune,
thank you very much for creating a Pull Request!
Here is a small checklist to get this PR merged as quickly as possible:

• Do all subcommands / options which take arguments have the arg property (arg: {})?
• Are all options modular? E.g. a -u -x instead of -aux
• Have all other checks passed?

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[QuiiBz]

Thanks for your contribution! Love PlanetScale, they are doing an amazing job!

[gusfune]

Finished with all change requests by @QuiiBz. Those were very helpful, thanks!

[QuiiBz]

You're welcome, you've done a really great job! LGTM 🎉