feat: Add announcement support to update_assets tool

[mustafahasankhan]

Summary

Extends the update_assets tool to support creating, updating, and removing announcements on assets.

Changes

• Added ANNOUNCEMENT to UpdatableAttribute enum
• Added AnnouncementType enum and Announcement model
• Implemented announcement handling in update_assets using PyAtlan's native methods
• Updated tool documentation with examples

Usage

# Add announcement
update_assets_tool(
    assets={...},
    attribute_name="announcement",
    attribute_values=[{
        "announcement_type": "WARNING",
        "announcement_title": "Data Quality Issue",
        "announcement_message": "Missing records for Q4"
    }]
)

# Remove announcement  
update_assets_tool(
    assets={...},
    attribute_name="announcement",
    attribute_values=[None]  # or [{}]
)

Tested

Adding, editing and removingannouncement