Rename Release groups in issue_workflow.md

Based on https://about.gitlab.com/handbook/product/categories/#release-stage:
- 'core release' -> 'progressive delivery'
- 'supporting capabilities' -> 'release management'

doc/development/contributing/issue_workflow.md

@@ -154,8 +154,8 @@ The current group labels are:
 * ~"group::ci and runner" 
 * ~"group::testing" 
 * ~"group::package" 
-* ~"group::core release" 
-* ~"group::supporting capabilities" 
+* ~"group::progressive delivery" 
+* ~"group::release management" 
 * ~"group::autodevops and kubernetes" 
 * ~"group::serverless and paas"
 * ~"group::apm"