Add a circuit breaker to the size of the state object in Task Manager tasks

[mikecote]

Problem Statement

We have no guardrails when it comes to storing state within a Task Manager task, allowing some implementations to abuse what is stored within the state, causing the Task Manager performance to degrade by serializing / deserializing large amounts of data during the claiming phase.

We should start by logging a warning when we save a task with a state larger than 1 MB. This will let us collect how frequently this is happening.

Definition of Done

• [ ] Warning message is logged when a task finishes running and has a state larger than 1 MB
• [ ] Warning message is logged when a task is scheduled and has a state larger than 1 MB
• [ ] Warning message includes the configured limit (1 MB)
• [ ] Warning message include the observed size (X MB)

[elasticmachine]

Pinging @elastic/response-ops (Team:ResponseOps)