Audit Log entries when a member's team role changes

### Problem Statement

A customer of ours would like for the audit log to show when a member's team role changes. Right now, we only have entries for org role changes (listed under the "member.edit" category).

### Solution Brainstorm

Create a new category for team role changes

### Product Area

Settings

Start by tracing the existing org role audit entries and the "member.edit" category in the Sentry codebase. Determine where team role changes are recorded and how audit categories are defined. Done means a member's team role change creates a distinct audit log entry and category, with existing org role logging preserved.

Written by the indexing model from the issue text.