Add system_api_key to cloud config

[scsmithr]

Summary

In order to communicate with Cloud, we'll need an api key to identify the client making the request. The GlareDB side of this should be simple, we just need to add the key to the cloud config, and attach it to request in the Cloud Client.

Specifications

• Add api key to cloud config.
• Ensure the api key is attached to the request in Cloud Client.

Rationale

To authenticate with cloud

Impact

We'll need to configure and enable Cloud communication when spinning up pods in Cloud to see this working end to end.

Cloud would provide api key via GLAREDB__CLOUD__SYSTEM_API_KEY (might require some trial and error)

Tasks

See specs.

[scsmithr]

Opaque to GlareDB.

On Cloud: Do JWT like thing with the database id included in the message.

[scsmithr]

https://github.com/GlareDB/glaredb/blob/main/crates/pgsrv/src/handler.rs#L628