extend API filter to allow for "not starts with" operation

[konstan]

When searching for resources with the full-text search, it's sometimes handy to remove (filter out) certain documents from the search results by "not starts with" operation. We already have "starts with" as ^= (implemented as prefix https://www.elastic.co/guide/en/elasticsearch/reference/7.17/query-dsl-prefix-query.html). The syntax can eg. be !^= (i.e., negated prefix). Example: name!^='[SmartGrid]'.