feat(pii): Soft-deprecate `send_default_pii` + backwards-compatible mapping

[sl0thentr0py]

Stack position: 3/10. Blocked by #3000**.**

Keep send_default_pii working while making data_collection the single source of truth internally, so downstream wiring reads only data_collection.

Scope

• Emit a soft-deprecation warning when send_default_pii= is used.
• Map the legacy flag onto data_collection defaults:
  • send_default_pii = false → conservative/restricted categories (current Ruby default)
  • send_default_pii = true → spec-permissive set (collect user identity, bodies, cookies, query params, db params)
• Precedence: an explicitly-configured data_collection category wins over the legacy flag.
• Provide a single internal resolver (e.g. configuration.data_collection fully-resolved) that all instrumentation reads — no code should branch on the raw send_default_pii boolean after this PR.
• Update the doc comment block at sentry-ruby/lib/sentry/configuration.rb:229-235.

Files

• sentry-ruby/lib/sentry/configuration.rb
• sentry-ruby/spec/sentry/configuration_spec.rb

Tests

• Mapping for true / false; explicit data_collection overrides legacy flag; deprecation notice emitted once.

[linear-code]

RUBY-190