fix: update issue template branch references from master to main

- Update sync-plugin-docs.yml description (line 40)
- Update placeholder from 'master' to 'main' (line 41)
- Update default value from 'master' to 'main' (line 42)
- Add influxdb3_plugins/ to .gitignore
- Ensures template matches influxdb3_plugins default branch

Author: MeelahMe

.github/ISSUE_TEMPLATE/sync-plugin-docs.yml

@@ -37,9 +37,9 @@ body:
       label: Source Commit/Branch
       description: |
         Commit SHA, branch name, or tag from influxdb3_plugins repository to sync from.
-        Leave as `master` to sync from the latest main branch.
-      placeholder: "master"
-      value: "master"
+        Leave as `main` to sync from the latest main branch.
+      placeholder: "main"
+      value: "main"
     validations:
       required: true
 

.gitignore

@@ -38,3 +38,4 @@ tmp
 # User context files for AI assistant tools
 .context/*
 !.context/README.md
+influxdb3_plugins/