fix(compute_ctl): Only offload LFC state if no prewarming is in progress (#12645)

## Problem

We currently offload LFC state unconditionally, which can cause
problems. Imagine a situation:
1. Endpoint started with `autoprewarm: true`.
2. While prewarming is not completed, we upload the new incomplete
state.
3. Compute gets interrupted and restarts.
4. We start again and try to prewarm with the state from 2. instead of
the previous complete state.

During the orchestrated prewarming, it's probably not a big issue, but
it's still better to do not interfere with the prewarm process.

## Summary of changes

Do not offload LFC state if we are currently prewarming or any issue
occurred. While on it, also introduce `Skipped` LFC prewarm status,
which is used when the corresponding LFC state is not present in the
endpoint storage. It's primarily needed to distinguish the first compute
start for particular endpoint, as it's completely valid to do not have
LFC state yet.

compute_tools/src/http/openapi_spec.yaml

@@ -613,11 +613,11 @@ components:
         - skipped
       properties:
         status:
-          description: Lfc prewarm status
-          enum: [not_prewarmed, prewarming, completed, failed]
+          description: LFC prewarm status
+          enum: [not_prewarmed, prewarming, completed, failed, skipped]
           type: string
         error:
-          description: Lfc prewarm error, if any
+          description: LFC prewarm error, if any
           type: string
         total:
           description: Total pages processed
@@ -635,11 +635,11 @@ components:
         - status
       properties:
         status:
-          description: Lfc offload status
+          description: LFC offload status
           enum: [not_offloaded, offloading, completed, failed]
           type: string
         error:
-          description: Lfc offload error, if any
+          description: LFC offload error, if any
           type: string
 
     PromoteState: