feat(eap): Produce spans to the items topic

[phacops]

To do:

• Add span.data to the attributes
• Add missing root fields to attributes
• Add missing attributes added in the current Snuba consumer
• Fix integration tests
• Produce the JSON-encoded span to ingest-spans

[jan-auer]

This will be done in the buffer instead:
getsentry/sentry#91714

Differences from this implementation:

• Maps hash to sentry.hash
• Includes sub-second parts in timestamps

[phacops]

This will not move forward, we'll stick with the buffer producing to snuba-items directly.

[Dav1dde]

As discussed, to make the transition possible from one topic to the other (with a different item format), we implement a double write, with an optional config flag to disable/enable the snuba-spans and snuba-items topics.

We cannot always double write, because that means we will double produce to clickhouse (as the buffer writes to snuba-items) as well.