DX-2255: Allow Metadata in Filter

[CahidArda]

Made it possible to pass metadata fields in filters:

const results = await searchIndex.search({
  query: "test-data",
  limit: 2,
  filter: {
    AND: [{ text: { glob: "*test-data*" } }, { "@metadata.count": { greaterThanOrEquals: 3 } }],
  },
  semanticWeight: 0.5,
  inputEnrichment: false,
});

[linear]

DX-2255 search-js - allow metadata filters with @metadata prefix