Refine the urgencies defined for GraphQL queries

In #331697 (closed) we've added apdex metrics for GraphQL. These currently all use a default target duration of 1 second coming from the default urgencies we've defined for requests

Now, we should revisit these urgencies and make them configurable by the groups that own them. Looking at the overall distribution, most queries perform way faster than requests: https://log.gprd.gitlab.net/goto/c4c06910-6d78-11ec-bf16-136dbae1ae92

My proposal would be to have the following

Urgency	Target duration	Cumulative percentage of traffic	Note
High	0.25s	99.463%
default	0.5s	99.594%	Default for known requests from our frontend
medium	1s	99.69%
low	5s	99.991%	Default for unknown requests from external clients

To customize an urgency for a known requests, we could allow specifying this using a magic comment in the .graphql query file.