Set 'High' Custom Error Budget Thresholds

This is one part of the work from #345335 (closed) (comment 740451691) that we need to do.

These endpoints needs to be set as High urgency based on the historical data below.

See https://docs.gitlab.com/ee/development/application_slis/rails_request_apdex.html for the instruction.

	json.meta.caller_id.keyword: Descending	99.5th percentile of json.duration_s	99.8th percentile of json.duration_s	Count
1	graphql:mergeRequestLabels	0.00026942999102175200	0.00026942999102175200	2
2	graphql:getDashboardValidationWarnings	0.00043397501576691900	0.00043397501576691900	2
3	graphql:mergeRequestTimeTracking	0.0004734156635752130	0.0006740397061340750	5322742
4	graphql:mergeRequestSubscribed	0.00047537544880761000	0.0006782092779657010	5275073
5	graphql:getMrParticipants	0.0004804545459429870	0.0006831730198918380	5322282
6	graphql:mergeRequestReference	0.000491920012490351	0.0007012479307028570	5322286
7	graphql:projectMilestones	0.0005866040010005240	0.0007207749318331470	2990
8	graphql:workInProgress	0.0005346121210300110	0.0007541982795468020	292449
9	graphql:mergeRequestMilestone	0.000536959263757827	0.0007556862075965840	5322283
10	graphql:autoMergeEnabledEE	0.0005994645090759910	0.0008284298577652940	206632
11	graphql:unknown	0.0006268674166029070	0.0008377012101002140	106861
12	graphql:mergeRequestTodos	0.0006223237565859260	0.0008418364205463770	5275037
13	graphql:getState	0.0006217798656288690	0.0008439281677994000	64620688
14	graphql:readyToMergeEE	0.0006278052293069360	0.0008480925551809450	22145081
15	graphql:securityReportDownloadPaths	0.0006246108518357220	0.0008512802582300880	2678788
16	graphql:userPermissionsQuery	0.0006243445613453580	0.0008517345139989700	291316
17	graphql:mergeRequestSidebarDetails	0.0006267121777115810	0.0008526805534394540	5324899
18	graphql:getMergeRequestState	0.0006325084272266520	0.0008587523832191880	5354144
19	graphql:mrUserPermission	0.000631861105292207	0.0008591671199030340	282489
20	graphql:rebaseQuery	0.0006450574963628020	0.0008702750508662470	180188
21	graphql:mergeRequest	0.0006226692193498220	0.0009635383181739470	24360
22	graphql:mrTimeTrackingReport	0.0019350330112502000	0.0019350330112502000	23
23	HEAD /api/:version/projects/:id/merge_requests/:merge_request_iid/award_emoji	0.0027600000612437700	0.0027600000612437700	79
24	GroupsController#unfoldered_environment_names	0.04554999992251400	0.04554999992251400	3
25	ProjectsController#unfoldered_environment_names	0.05649999901652340	0.05649999901652340	22
26	HEAD /api/:version/projects/:id/merge_requests/:merge_request_iid	0.06684000045061110	0.06684000045061110	3
27	Projects::MergeRequestsController#delete_description_version	0.07101000100374220	0.07101000100374220	6
28	Projects::MergeRequestsController#export_csv	0.07165999710559850	0.07165999710559850	61
29	GET /api/:version/projects/:id/merge_requests/:merge_request_iid/context_commits	0.11856000125408200	0.11856000125408200	6