chore: update stale pr workflow (#33537)

### Issue # (if applicable)

Closes #<issue number here>.

### Reason for this change

Messaging around stale PRs isn't clear, contributors don't always know what the next steps are if their PR is considered stale. 

Also, response time for contributors is too short. IMO 7 days isn't enough to get back to our comments as we sometimes take a long time to review PRs. Open to discussion on what the window for response time should be



### Description of changes



### Describe any new or updated permissions being added


- Update which labels which should be skipped for stale PRs
- Update merge conflict warning to be more clear about next steps
- Update time given to contributors to respond




### Description of how you validated changes



### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

.github/workflows/close-stale-prs.yml

@@ -19,10 +19,18 @@ jobs:
           # appropriately.
           github-token: ${{ secrets.PROJEN_GITHUB_TOKEN }}
           stale-days: 21
-          response-days: 7
+          response-days: 14
 
           # Optional
           important-checks-regex: AutoBuildv2Project1C6BFA3F
+          merge-conflict-warning: |
+            This PR cannot be merged because it has conflicts. Please resolve them. Note that PRs with merge conflicts considered stale and will be closed if not resolved.
+
+            To prevent automatic closure:
+            - Fix merge conflicts
+            - OR request an exemption by adding a comment containing 'Exemption Request' with justification e.x "Exemption Request: <justification>"
+            - OR request clarification by adding a comment containing 'Clarification Request' with a question e.x "Clarification Request: <question>"
+
           warn-message: |
             This PR has been in the STATE state for 3 weeks, and looks abandoned. Note that PRs with failing linting check or builds are not reviewed, please ensure your build is passing 
             
@@ -31,8 +39,8 @@ jobs:
             - OR request an exemption by adding a comment containing 'Exemption Request' with justification e.x "Exemption Request: <justification>"
             - OR request clarification by adding a comment containing 'Clarification Request' with a question e.x "Clarification Request: <question>"
 
-            This PR will automatically close in 7 days if no action is taken.
+            This PR will automatically close in 14 days if no action is taken.
 
           close-message: This PR has been deemed to be abandoned, and will be automatically closed. Please create a new PR for these changes if you think this decision has been made in error.
-          skip-labels: contribution/core,pr-linter/do-not-close,pr/needs-maintainer-review,pr-linter/exemption-requested
+          skip-labels: contribution/core,pr-linter/do-not-close,pr/needs-maintainer-review,pr-linter/exemption-requested,pr/reviewer-clarification-requested,pr/needs-community-review,pr/work-in-progress
           close-label: closed-for-staleness