Set GitHub topics and repo description via .asf.yaml

The repo had no topics and a description of "Apache Axis2-C", so it does not
surface for anyone browsing or searching GitHub for a C framework doing JSON,
REST, httpd modules, HTTP/2, Android or MCP. Adds 16 labels and a description
naming what the framework actually does.

Purely additive; the existing homepage and branch-protection ruleset are
unchanged. Topics apply once ASF infrastructure processes this on the default
branch.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>