Add OTLP logs endpoint

[AbhiPrasad]

Notion doc: https://www.notion.so/sentry/Logs-OTLP-Endpoint-2638b10e4b5d8050a147d0dd46df1915

Tracking issue: getsentry/sentry#98649.

To help deliver on Log Drains for Cloudflare (getsentry/sentry#95913), which we've identify as a high priority item for the logging product, we'd like to add an OTLP endpoint for logs to Relay.

Here's a vibe coded approximate PR to get an idea of the surface area impacted and parts of relay we need to think about: #5110.

The approximate steps in Relay looks like:

1. Adding feature flags for the feature so we can gate the release/rollout
2. Bringing back the otel log -> sentry log transform that was removed in ref(ourlogs): Removes support for the envelope otel log item type #5082
3. Adding a OtelLogsData item type (and corresponding boilerplate)
4. Add an otel log endpoint ("/api/{project_id}/otlp/v1/logs/") alongside code in the ourlogs processor that handles OtelLogsData

We'll also need to update https://github.com/getsentry/sentry/blob/master/src/sentry/api/serializers/models/project_key.py to add a new otlp logs field to the dsn model.

[linear]

RELAY-153 Add OTLP logs endpoint