OBS: Create SLOs for Send

[aatchison]

• Use SLO document template: https://github.com/thunderbird/observability-strategy/blob/main/docs/rfc/infrastructure_monitoring/slo_template.md
• Populate SLO document in https://github.com/thunderbird/observability-strategy/tree/main/services
• Take inventory of all mentioned services, infrastructure, dependencies, etc. and add more if needed
• Create SLOs for monitor-able services.
• Modify template as needed and add any notes as needed.

[aatchison]

Basic document is ready for review here:
https://github.com/thunderbird/observability-strategy/blob/main/services/send.md