Test the upcoming extended schema of the EvP events associated to
symdb uploads and the matching fields in the gzipped attachment body.
The new test is initially "missing_feature" for every tracer; once the
different tracers are released, the manifest entries can be moved off
"missing_feature" to a version cap.

The event JSON gets the following fields at the root, in camelCase to
match the rest of the EvP event schema:

• "ddsource" (was already required)
• "service" (was already required)
• "version"
• "language"
• "runtimeId" (was already required)
• "type": "symdb"
• "uploadId"
• "batchNum" (1-indexed integer)
• "final" (boolean)
• "attachmentSize" (positive integer)

The attachment body gets the matching upload metadata at the root, in
snake_case to match the rest of the attachment scope schema
(scope_type, source_file, ...):

• "upload_id"
• "batch_num"
• "final"

The test also cross-checks per upload that uploadId/batchNum in the
event equal upload_id/batch_num in the attachment.

The schema (utils/interfaces/schemas/library/symdb/v1/input-request.json)
keeps the original "ddsource"/"service"/"runtimeId" as required and
type-checks the new fields if present, so existing tracer versions are
not regressed by the schema. The strict presence check lives in the new
test_event_metadata method, which is gated per tracer/agent version via
the manifests.

Test harness changes:

• BaseDebuggerTest gains a symdb_upload_events list field.
• A new _collect_symdb_upload_events() walks every captured
  /symdb/v1/input request, picks the multipart parts whose
  Content-Disposition has name="event", and stores the parsed JSON.
• collect() invokes it alongside _collect_symbols().

🛟 #apm-shared-testing 🛟

Reviewer checklist

• Anything but tests/ or manifests/ is modified ? I have the approval from R&P team
• A docker base image is modified?
  • the relevant build-XXX-image label is present
• A scenario is added, removed or renamed?
  • Get a review from R&P team