Add morelikethis a non-greedy version of the morelike keyword
morelike is a keyword that cannot be combined because it is greedy
and considered a query header. This does not allow to combine it
with any other keywords/query text.
Since morelike is heavily used it is not possible to fix without
breaking existing clients.
Introduce a new keyword "morelikethis" to address all the limitations
Like any other keywords its value must be wrapped in double quotes if
it contains space.
Internally it will act as a more_like feature:
- be reported as such in metrics
- cached using the same TTL config