Add /terminate API (#6745)

this is to speed up suspends, see
https://github.com/neondatabase/cloud/issues/10284

## Problem

## Summary of changes

## Checklist before requesting a review

- [ ] I have performed a self-review of my code.
- [ ] If it is a core feature, I have added thorough tests.
- [ ] Do we need to implement analytics? if so did you add the relevant
metrics to the dashboard?
- [ ] If this PR requires public announcement, mark it with
/release-notes label and add several sentences in this section.

## Checklist before merging

- [ ] Do not forget to reformat commit message to not include the above
checklist

compute_tools/src/http/openapi_spec.yaml

@@ -168,6 +168,29 @@ paths:
               schema:
                 $ref: "#/components/schemas/GenericError"
 
+  /terminate:
+    post:
+      tags:
+      - Terminate
+      summary: Terminate Postgres and wait for it to exit
+      description: ""
+      operationId: terminate
+      responses:
+        200:
+          description: Result
+        412:
+          description: "wrong state"
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/GenericError"
+        500:
+          description: "Unexpected error"
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/GenericError"
+
 components:
   securitySchemes:
     JWT: