Python: Add init file to connectors submodule (#2350)

### Motivation and Context
Microsoft docs autogeneration will not recognize connectors as a
submodule of semantic_kernel unless it has an __init__.py file

### Description

Adds an empty __init__.py file to semantic_kernel/connectors/ - will not
affect module imports for this package but will ensure that connectors
is correctly picked up as a semantic_kernel submodule.

### Contribution Checklist

<!-- Before submitting this PR, please make sure: -->

- [ ] The code builds clean without any errors or warnings
- [ ] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [ ] All unit tests pass, and I have added new tests where possible
- [ ] I didn't break anyone 😄

---------

Co-authored-by: Dmytro Struk <[email protected]>
Co-authored-by: Abby Harrison <[email protected]>

python/semantic_kernel/connectors/__init__.py

@@ -0,0 +1 @@
+# Copyright (c) Microsoft. All rights reserved.