[FTS] REST: Validate index definition if char_filter and token_filter is passed as an array

We need a validation for the index definition where custom analysers are used to see if the char_filter and token_filters are passed as arrays. Currently, it allows a string to be set for char_filter and token_filter instead of an array, and the index gets created.

"analysis": {
"analyzers": {
"customAnalyzer1":

{ "type": "custom", "char_filters": "html", "tokenizer": "web", "token_filters": "to_lower" }

}
}