Issue forms: add optional source connector, make destination optional

Issues can be source-side (e.g. a Postgres CDC bug/feature) with no relevant
destination. GitHub issue forms have no conditional fields, so add a separate
optional "Source connector" dropdown alongside the destination one and mark
both as fill-in-if-applicable. The destination dropdown keeps its exact label
(the deprecation-triage workflow parses it) and now is optional, so source-only
issues aren't forced to pick a destination.

Refs #4465

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Jeremyyang920

.github/ISSUE_TEMPLATE/bug_report.yml

@@ -38,6 +38,20 @@ body:
     validations:
       required: true
 
+  - type: dropdown
+    id: source_connector
+    attributes:
+      label: Source connector
+      description: If this issue relates to a source connector, select it here. Leave blank if not applicable.
+      options:
+        - Postgres
+        - MySQL
+        - MongoDB
+        - BigQuery
+        - Other
+    validations:
+      required: false
+
   - type: markdown
     attributes:
       value: |
@@ -51,7 +65,7 @@ body:
     id: destination_connector
     attributes:
       label: Destination connector
-      description: Which destination connector is affected? (See the deprecation notice above.)
+      description: If this issue relates to a destination connector, select it here (see the deprecation notice above). Leave blank if not applicable.
       options:
         - ClickHouse
         - ClickHouse Cloud
@@ -65,6 +79,6 @@ body:
         - Confluent
         - Azure Event Hubs
         - Google Pub/Sub
-        - Other / N/A
+        - Other
     validations:
-      required: true
+      required: false

.github/ISSUE_TEMPLATE/feature_request.yml

@@ -33,6 +33,20 @@ body:
     validations:
       required: false
 
+  - type: dropdown
+    id: source_connector
+    attributes:
+      label: Source connector
+      description: If this request relates to a source connector, select it here. Leave blank if not applicable.
+      options:
+        - Postgres
+        - MySQL
+        - MongoDB
+        - BigQuery
+        - Other
+    validations:
+      required: false
+
   - type: markdown
     attributes:
       value: |
@@ -44,9 +58,8 @@ body:
     id: destination_connector
     attributes:
       label: Destination connector
-      description: Which destination connector does this relate to? (See the deprecation notice above.)
+      description: If this request relates to a destination connector, select it here (see the deprecation notice above). Leave blank if not applicable.
       options:
-        - Not applicable
         - ClickHouse
         - ClickHouse Cloud
         - Postgres
@@ -61,4 +74,4 @@ body:
         - Google Pub/Sub
         - Other
     validations:
-      required: true
+      required: false