### Description

Before ES 7.x it was possible to provide a list of fields by URL or BODY request for field_caps API.
https://www.elastic.co/guide/en/elasticsearch/reference/6.8/search-field-caps.html
`POST _field_caps
{
   "fields" : ["rating"]
}`

Starting from 7.x this feature was removed, and only one possible way it uses URI but in this case, it is possible to have an error 414 (Request-URI Too Long).

I would like to return this feature back.
server/src/test/java/org/elasticsearch/action/fieldcaps/FieldCapabilitiesRequestTests.java
request.getDescription().length(),
            lessThanOrEqualTo(1024 + ("indices[x,y,z], fields[" + "s9999,... (9999 in total, 9999 omitted)], filters[], types[]").length())
        );
        request.fields("a");
        request.indices(lots);
        assertThat(
            request.getDescription(),
            allOf(
                startsWith("indices[s0,s1,s2,s3"),
                containsString("..."),
                containsString(lots.length + " in total"),
                containsString("omitted"),
                endsWith("], fields[a], filters[], types[]")
            )
        );
        assertThat(
            request.getDescription().length(),
            lessThanOrEqualTo(1024 + ("indices[" + "s9999,... (9999 in total, 9999 omitted)], fields[a], filters[], types[]").length())
        );
        final FieldCapabilitiesRequest randomRequest = createTestInstance();
        final String description = randomRequest.getDescription();
        for (String index : randomRequest.indices()) {
            assertThat(description, containsString(index));
        }
        for (String field : randomRequest.fields()) {
            assertThat(description, containsString(field));
        }
    }
}