feat: add PR welcome message workflow (#640)

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: AJ Steers <aj@airbyte.io>

Author: devin-ai-integration[bot]

.github/pr-welcome-community.md

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+## 👋 Welcome to the Airbyte Python CDK!
+
+Thank you for your contribution from **{{ .repo_name }}**! We're excited to have you in the Airbyte community.
+
+### Testing This CDK Version
+
+You can test this version of the CDK using the following:
+
+```bash
+# Run the CLI from this branch:
+uvx 'git+https://github.com/airbytehq/airbyte-python-cdk.git@{{ .branch_name }}#egg=airbyte-python-cdk[dev]' --help
+
+# Update a connector to use the CDK from this branch ref:
+cd airbyte-integrations/connectors/source-example
+poe use-cdk-branch {{ .branch_name }}
+```
+
+### Helpful Resources
+
+- [Contributing Guidelines](https://docs.airbyte.com/contributing-to-airbyte/)
+- [CDK API Reference](https://airbytehq.github.io/airbyte-python-cdk/)
+
+### PR Slash Commands
+
+As needed or by request, Airbyte Maintainers can execute the following slash commands on your PR:
+
+- `/autofix` - Fixes most formatting and linting issues
+- `/poetry-lock` - Updates poetry.lock file
+- `/test` - Runs connector tests with the updated CDK
+
+If you have any questions, feel free to ask in the PR comments or join our [Slack community](https://airbytehq.slack.com/).
+

.github/pr-welcome-internal.md

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+## 👋 Greetings, Airbyte Team Member!
+
+Here are some helpful tips and reminders for your convenience.
+
+### Testing This CDK Version
+
+You can test this version of the CDK using the following:
+
+```bash
+# Run the CLI from this branch:
+uvx 'git+https://github.com/airbytehq/airbyte-python-cdk.git@{{ .branch_name }}#egg=airbyte-python-cdk[dev]' --help
+
+# Update a connector to use the CDK from this branch ref:
+cd airbyte-integrations/connectors/source-example
+poe use-cdk-branch {{ .branch_name }}
+```
+
+### Helpful Resources
+
+- [CDK API Reference](https://airbytehq.github.io/airbyte-python-cdk/)
+
+### PR Slash Commands
+
+Airbyte Maintainers can execute the following slash commands on your PR:
+
+- `/autofix` - Fixes most formatting and linting issues
+- `/poetry-lock` - Updates poetry.lock file
+- `/test` - Runs connector tests with the updated CDK
+- `/poe <command>` - Runs any poe command in the CDK environment
+
+[📝 _Edit this welcome message._](https://github.com/airbytehq/airbyte-python-cdk/blob/main/.github/pr-welcome-internal.md)

.github/workflows/welcome-message.yml

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+name: Community PR Welcome Message
+
+# This workflow automatically adds a welcome message to PRs from community contributors (forks)
+# It includes CDK usage instructions and other helpful resources for testing changes
+#
+# MANUAL TESTING INSTRUCTIONS:
+# To manually test this workflow, temporarily uncomment the "synchronize" event type as a workflow trigger.
+# Then the workflow will run for all new commits.
+#
+# Before merging, remember to again comment-out the "synchronize" clause and uncomment the `if:` condition.
+
+on:
+  pull_request:
+    types:
+      - opened
+      - reopened
+      # Toggle this line, uncommenting for testing:
+      # - synchronize
+
+jobs:
+  welcome-contributor:
+    name: PR Welcome Message
+    permissions:
+      contents: read
+      issues: write
+      pull-requests: write
+    runs-on: ubuntu-24.04
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Render template
+        id: template
+        uses: chuhlomin/render-template@v1.4
+        with:
+          # Use a different template for internal vs forks (community)
+          template: ${{ github.event.pull_request.head.repo.fork == true && '.github/pr-welcome-community.md' || '.github/pr-welcome-internal.md' }}
+          vars: |
+            repo_name: ${{ github.event.pull_request.head.repo.full_name }}
+            branch_name: ${{ github.event.pull_request.head.ref }}
+
+      - name: Create comment
+        uses: peter-evans/create-or-update-comment@v4
+        with:
+          issue-number: ${{ github.event.pull_request.number }}
+          body: ${{ steps.template.outputs.result }}