Create AzDO PR templates for internal/* branches (#37917)

- follow-up to 9ca2be8
- the branches/ files are _prefix_ matched against PR target branches
  - "The name must match the first level of the branch name"
  - see <https://docs.microsoft.com/en-us/azure/devops/repos/git/pull-request-templates#branch-specific-pull-request-templates>
- note: these templates are only read from the default branch

nit: provide default PR template for the odd case of an internal PR targeting 'main' or a temporary (feature) branch
  - see <https://docs.microsoft.com/en-us/azure/devops/repos/git/pull-request-templates#default-pull-request-templates>
  - keep minimal.md PR template separate from the default
  - this template helps after removing servicing template for internal `tell-mode` PRs
  - default PR template can't be used as an additional PR template
    - see <https://docs.microsoft.com/en-us/azure/devops/repos/git/pull-request-templates#additional-pull-request-templates>

Author: dougbu

.azuredevops/pull_request_template.md

@@ -0,0 +1,9 @@
+# {PR title}
+
+Summary of the changes (Less than 80 chars)
+
+## Description
+
+{Detail}
+
+Fixes #{bug number} (in this specific format)

.azuredevops/pull_request_template/branches/internal.md

@@ -0,0 +1,45 @@
+# {PR title}
+
+Summary of the changes (Less than 80 chars)
+
+## Description
+
+{Detail}
+
+Fixes #{bug number} (in this specific format)
+
+## Customer Impact
+
+{Justification}
+
+## Regression?
+
+- [ ] Yes
+- [ ] No
+
+[If yes, specify the version the behavior has regressed from]
+
+## Risk
+
+- [ ] High
+- [ ] Medium
+- [ ] Low
+
+[Justify the selection above]
+
+## Verification
+
+- [ ] Manual (required)
+- [ ] Automated
+
+## Packaging changes reviewed?
+
+- [ ] Yes
+- [ ] No
+- [ ] N/A
+
+----
+
+## When servicing release/2.1
+
+- [ ] Make necessary changes in eng/PatchConfig.props

.azuredevops/pull_request_template/minimal.md

@@ -1,7 +1,7 @@
 # {PR title}
 
 <!--
-  Use for tell mode PRs after removing servicing template. Ignoring internal PRs targeting main (extreme corner case).
+  Use for tell mode PRs after removing servicing template.
 -->
 
 Summary of the changes (Less than 80 chars)