feat: auto-apply labels to DNS check PRs

[Timeraa]

Summary

Automatically applies appropriate labels to PRs created by the DNS check workflow based on what changes were made.

Changes

• Enhanced CLI to output metadata about DNS check results (deletions, updates, multiple activities)
• Updated DNS check workflow to use the built-in labels parameter from peter-evans/create-pull-request

Label Logic

• repo maintenance - Always applied (automated maintenance)
• activity deletion - Applied when activities are removed
• activity update - Applied when activities are updated
• multiple activities - Applied when 2+ activities are affected

Examples

Scenario	Labels Applied
1 activity deleted	repo maintenance, activity deletion
1 activity updated	repo maintenance, activity update
2+ activities affected	All relevant labels + multiple activities