Additional validations + use inferenceBlockheight in NetworkInferences

[xmariachi]

Purpose of Changes and their Description

• Additional validations on validations.go

  • nonempty infererValues is required
  • input data blockheight is required to be non-nil and non-zero
  • inference and forecasts blockheight need to be aligned with bundle blockheight

• fix usage of current block ctx.Blockheight() in inferenceBlockheight in NetworkInferences responses.

Are these changes tested and documented?

• If tested, please describe how. If not, why tests are not needed. -- unit tests fixed + cases added.
• If documented, please describe where. If not, describe why docs are not needed. -- no need to document, not relevant functional changes.
• Added to Unreleased section of CHANGELOG.md?

[amimart]

LGTM