agent code quality improvement

MR: pending

Description

There are two points raised during the agent MR review. And we would like to work on as an improvement in code quality.

• Instead of the current approach, I recommend to define the response, etc as a proto and use the validator to ensure things are within expected bounds to avoid any surprises. See how gitlab/api package does that. This can be done in a follow up if you decide to go down this path. gitlab-org/cluster-integration/gitlab-agent!1495 (comment 1924069413)
• ry to avoid mutable fields where possible. They make it easier to introduce a bug. gitlab-org/cluster-integration/gitlab-agent!1495 (comment 1926240459)

Acceptance Criteria

• address both comments

Technical Requirements

N/A

Design Requirements

None, no UI impact.

Impact Assessment

• Instance admins may want to override these values to either provide faster update and reconciliation for workspaces, or to reduce load on the monolith.
• Developers may want to override these values so they can have faster feedback when developing features, e.g. have a much faster full reconciliation interval than an hour. Otherwise they have to hack the hardcoded intervals, or restart their agent to force a full reconcile.