filters: `!=` support for arrays of values

[benhowes]

Describe the bug
When using filters, I was expecting != to allow filtering for when a value was not in an array, given that = allows for filtering where an array contains.

Having read up in #611 I thought that would be the behaviour.

To Reproduce
Steps to reproduce the behavior:

1. Create a document schema containing an array of values
2. Perform a search with a filter contain arrayValue != "someValue"
3. It seems that any document which contains an element which is not "someValue" will be returned to the client.

Additional context
I have been able to use NOT (arrayValue = "someValue") to satisfy my usecase for the time being.

It may just be that you do a documentation update to make the behaviour with filters on arrays a bit more clear to meili-n00bs like me :)

[curquiza]

Fixed by the integration of the new search engine in #1421