[SLO] [Alert] Add service and transaction fields in SLO burn rate alert

[benakansara]

Resolves #243092

Adds following fields in SLO burn rate alert when they are available in SLO summary:

• service.name
• service.environment
• transaction.type
• transaction.name

How to test

1. Create APM latency or APM availability SLO
2. Select a value in one or more of these fields - Service name, service environment, transaction type, transaction name
3. Confirm that selected values are included in alert document under service.name, service.environment, transaction.type and transaction.name

[elasticmachine]

Pinging @elastic/obs-ux-management-team (Team:obs-ux-management)

[kdelemme]

Tested locally and work as expected. Just a nit but otherwise looks good to me

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: ced38d4

Metrics [docs]

✅ unchanged

cc @benakansara