Prevent extra fields in index settings

[pandu-k]

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

• What is the current behavior? (You can also link to an open issue here)
  [BUG] validate index settings for models #341

• What is the new behavior (if this is a feature change)?
  Extra fields in the root and index_default fields in index settings fail validation.

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)
  No

• Have unit tests been run against this PR? (Has there also been any additional testing?)
  Todo

• Related Python client changes (link commit/PR here)
  n/a

• Related documentation changes (link commit/PR here)
  n/a

• Other information:

• Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes/features)
• Docs have been added / updated (for bug fixes / features)

[pandu-k]

unit tests: https://github.com/marqo-ai/marqo/actions/runs/4311061797