[SLO] Create introductory blog post for SLOs

[CoenWarmer]

📝Summary

Let's create a blog post for the SLO functionality we want to release in version 8.8.0. This can be shared on the Elastic website, with people in the field and through other marketing channels.

✅ Acceptance criteria

• It should describe most of the concepts surrounding SLOs: what is an SLO, what is an SLI, what are the different budgeting methods (timeslices / occurences). Lets make the connection with Google's SRE literature, so customers understand these are industry terms.
• It should describe why a customer would want to create an SLO: what does it offer to a business? what benefits does it offer SREs?
• It should describe the rule functionality, and make the connection with Kibana's Alerting functionality
• It should describe how a customer could create an SLO with Kibana 8.8.0.
• It should describe how a customer could create rules to be alerted when something happens with their SLOs.
• It should contain screenshots of the UI, describing each scenario (creating SLOs, creating rules).

[elasticmachine]

Pinging @elastic/actionable-observability (Team: Actionable Observability)

[kdelemme]

One of many of the potential blog post we can write: https://docs.google.com/document/d/1mG6lzOPzcUv0DYbYevCvk-edCbbdGrAB2CCy86qunjA/edit?pli=1#heading=h.srngnsfzoty0

[elasticmachine]

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