update errors cause param type

[CatchMe2]

Changes

• change Internal and Public error cause type to unknown
• add generic for PublicError (to be consistent with InternalError) - it will be breaking for any `if (err instanceof
• update Readme with cause param

Migration guide

Any instanceof check for PublicNonRecoverableError has to be modified (applies only if isPublicNonRecoverableError wasn't used). Please change:

if (err instanceof PublicNonRecoverableError) { ... }

into

if (isPublicNonRecoverableError(err)) { ... }

Checklist

• Apply one of following labels; major, minor, patch or skip-release
• I've updated the documentation, or no changes were necessary
• I've updated the tests, or no changes were necessary