Add CHANGELOG for 1.4.4 release

[philippjfr]

This release primarily addresses a critical regression in notebook comm channel handling introduced in 1.4.3 and includes a few minor fixes for Tabulator and documentation related issues. Many thanks to @justinwiley for his first contribution to Panel, @twobitunicorn as a returning contributor and the core contributors @maximlt and @philippjfr for their continued work.

Bug fixes

• Fix notebook CommManager extraction of buffers (#6880)
• Fix issue when editing timezone-aware datetime column Tabulator (#6879)
• Ensure Tabulator does not rebuild children when using embed_content with row_content (#6881)

Documentation

• Update OAuth documentation to correctly reference auth_code provider (#6875)
• Fix CheckBoxGroup value type annotation in reference docs (#6877)