[projection] Pass Context values from Trigger down to the Job

[bounoable]

When triggering a projection schedule, the values provided with the Context are not available in the projection.Job (which is also a Context). This is because the projection schedules create a fresh Context for each projection job, and the Context passed to Schedule.Trigger() is only used to be able to cancel the trigger itself (not the projection job).

If projection jobs provided the values from the trigger context, it would be possible to provide dynamic options to a projection job.

Example

package example

import (
  "context"
  "time"

  "github.com/modernice/goes/projection"
  "github.com/modernice/goes/projection/schedule"
)

func example() {
  s := schedule.Continuously(...) // setup the projection schedule
  go s.Subscribe(context.Background(), applyJob)

  // wait a bit, then trigger the projection
  time.Sleep(3*time.Second)
  
  ctx := context.WithValue(context.Background(), "key", "value")

  s.Trigger(ctx)
}

func applyJob(ctx projection.Job) error {
  v := ctx.Value("key") // <- this currently returns null, should return "value"

  return nil
}