[ENHANCEMENT] Check if WPT metric exists for feature before trying to insert

When the WPT Consumer job was first created, we told it to look at the last 2 [years](https://github.com/GoogleChrome/webstatus.dev/blob/43a2f84e5916842b4b98f7705bede2538a229739/infra/ingestion/workflows.tf#L106) of runs every time the job. This was because the IDs were still being added and we wanted the job to backfill.

This leads to really long run times. Almost a full day.

This may contribute to the high spikes in traffic to WPT too.

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Possible solutions

We should probably add a capstone table similar to what we do for the UMA export job.

https://github.com/GoogleChrome/webstatus.dev/blob/43a2f84e5916842b4b98f7705bede2538a229739/infra/storage/spanner/migrations/000008.sql#L60-L65

The primary key would be a combination of the Web feature ID and the WPT Run ID.

Alternatively, we could look at the merging logic:

https://github.com/GoogleChrome/webstatus.dev/blob/43a2f84e5916842b4b98f7705bede2538a229739/lib/gcpspanner/wpt_run_feature_metric.go#L296-L316

If we detect there are no changes, we could emit no mutation. That could save us an insert.