Environment (Required on creation): Camunda online documentation

Description (Required on creation; please attach any relevant screenshots, stacktraces, log files, etc. to the ticket):

'root-process-instance-start', 'executed-decision-instances', and 'task-worker' are missing in the metrics REST API documentation as valid metric names to use even though these work in the Admin console as well as generic REST API calls

Steps to reproduce (Required on creation): Go to : https://docs.camunda.org/manual/latest/reference/rest/metrics/get-metrics-sum/ and https://docs.camunda.org/manual/latest/reference/rest/metrics/get-metrics-interval/ 

Observed Behavior (Required on creation): no 'root-process-instance-start', 'executed-decision-instances', and 'task-worker' as valid metrics

Expected behavior (Required on creation): to see them

Root Cause (Required on prioritization): just missing

Solution Ideas (Optional): I can create a branch, correct it, and generate a pull request

Hints (Optional):