Adding dev_slots to event

[royendo]

follow up to: #9070

Checklist:

• Covered by tests
• Ran it and it works as intended
• Reviewed the diff before requesting a review
• Checked for unhandled edge cases
• Linked the issues it closes
• Checked if the docs need to be updated. If so, create a separate Linear DOCS issue
• Intend to cherry-pick into the release branch
• I'm proud of this work!

[pjain1]

Do we allow multiple dev deployments? How are we planning emitting to Orb - through the admin billing reporter or directly from runtime instances? If through admin then will require some logic change in the billing metrics API sql for the case of multiple dev deployment as currently it groups by org_id, project_id, event_name and take max(value) which would collapse values for different dev deployments in one row (may be we need to group instance_id as well).

[royendo]

That is very true and yes we'll have multiple dev deployments; I see Benjamin assigned https://linear.app/rilldata/issue/PLAT-470/report-all-deployments-slot-usage-to-orb to you, do you want to merge this and work on that or should i close this out?

[pjain1]

This will be needed anyways, lets keep it open. I will merge it when an approach is finalized.

[royendo]

admin/deployments.go:

• Replaced projProdSlots / projDevSlots with a single projSlots + environment on DeploymentAnnotations
• NewDeploymentAnnotations now uses resolveSlots() to set one slots value and stores the environment
• ToMap() emits project_slots and environment instead of two mutually exclusive project_prod_slots / project_dev_slots

runtime/registry.go:

• Single project_slots annotation lookup, emits {env}_slots metric (preserving prod_slots / dev_slots metric names for billing
  compatibility)