Add scaladoc to codec annotations

[googley42]

Issue #203 has been implemented but it looks like there are missing scaladoc for the annotations:

... add and document these annotations inside zio.schema.annotation ...

[jdegoes]

/bounty $100

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Attempt	Started (GMT+0)	Solution
🟢 @iamorozov		#550

[iamorozov]

I would like to try this one

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[algora-pbc]

🎉🎈 @iamorozov has been awarded $100! 🎈🎊

[987Nabil]

@jdegoes @vigoo actually, for Scala 3 we can extract Scala doc at macro execution. But this ticket is now already rewarded and has a merged pr. Should we open a new issue?

[vigoo]

If we can capture it it would definitely be a nice feature