Query hint to influence Consistent Critical Read Filter

The Consistent Critical Read Filter has "ignore" and "match" settings for the config. Sometimes it might be handy or easier to specify which queries should be matched/ignored directly in the code. Query hints could enable this.

For example:

-- maxscale ccr=match

would tell maxscale to apply the ccr filter to the query, and

-- maxscale ccr=ignore

would tell maxscale to not apply the ccr filter