Rename needs-triage label to untriaged according org conventions (opensearch-project#129)

Signed-off-by: Aleksei Atavin <axeo@aiven.io>

Author: axeoman

.github/ISSUE_TEMPLATE/BUG_TEMPLATE.md

@@ -2,7 +2,7 @@
 name: 🐛 Bug report
 about: Create a report to help us improve
 title: '[BUG]'
-labels: bug, needs-triage
+labels: bug, untriaged
 assignees: ''
 ---
 

.github/ISSUE_TEMPLATE/FEATURE_REQUEST_TEMPLATE.md

@@ -2,7 +2,7 @@
 name: 🎆 Feature request
 about: Request a feature in this project
 title: '[FEATURE]'
-labels: enhancement, needs-triage
+labels: enhancement, untriaged
 assignees: ''
 ---
 **Is your feature request related to a problem?**

.github/ISSUE_TEMPLATE/PROPOSAL_TEMPLATE.md

@@ -2,7 +2,7 @@
 name: 💭 Proposal
 about: Suggest an idea for a specific feature you wish to propose to the community for comment
 title: '[PROPOSAL]'
-labels: proposal, needs-triage
+labels: proposal, untriaged
 assignees: ''
 ---
 ## What kind of business use case are you trying to solve? What are your requirements?