Default to requesting protobuf format on query path, and remove experimental status on flag

[charleskorn]

What this PR does

This PR makes two related changes:

• it makes the protobuf format the default format for the query path
• it removes the experimental status on the -query-frontend.query-result-response-format flag

Note that this does not change the default or experimental status of the equivalent flag for the ruler-query-frontend -> ruler path, -ruler.query-frontend.query-result-response-format.

Which issue(s) this PR fixes or relates to

#4104

Checklist

• [n/a] Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[krajorama]

LGTM, I wonder if we could just switch to protobuf and remove the option since json doesn't work for histograms?

[pracucci]

LGTM!

LGTM, I wonder if we could just switch to protobuf and remove the option since json doesn't work for histograms?

I think so, but I would wait until we run it longer in production (including the protobuf format in the ruler).