Fetch default options for ML processor config maps

[ohltyler]

Description

This PR adds functionality to dynamically fetch a list of options when configuring input / output maps for ML processors. Specifically, adds support for 3 scenarios:

1. List of document fields as values for input maps when the document form field is populated (ingest)
2. List of query fields as values for input maps when the query form is populated (search)
3. List of document fields as values for input maps when configuring ML search response processors. References the selected index's mappings to populate options, including the field mapping type.

Note the dropdown still allows custom options if users need (e.g., pulling out a single value from an array, aggregation via JSONPath, etc.).

More details

• adds docFields/queryFields/indexMappingFields as state vars in MLProcessorInputs to handle the options as mentioned above
• adds MIT-licensed flattie to flatten nested JSON objs. Used for getting all options (keys) of a document or query JSON which can be deeply nested.
• more type safety on the options props passed to the form components
• index fetching on SearchInputs base component so any index created from ingest, has all details available on the search form without requiring refresh. This is useful to fetch the index mappings to populate options for ML search response processors.
• replacing the default query path logic on ML search request processors to derive from the query itself instead of hardcoding

Demo video, showing the options visible in the 3 different contexts of ML processors (ingest, search req, search resp):

screen-capture.15.webm

Check List

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