Revert "remove removed Debug/getDebugChainHeads V1 (#4970)" (#5057)

This reverts commit 6ebcbbdf4e.

beacon_chain/rpc/rest_debug_api.nim

@@ -61,6 +61,13 @@ proc installDebugApiHandlers*(router: var RestRouter, node: BeaconNode) =
           RestApiResponse.jsonError(Http500, InvalidAcceptError)
     return RestApiResponse.jsonError(Http404, StateNotFoundError)
 
+  # https://ethereum.github.io/beacon-APIs/#/Debug/getDebugChainHeads
+  router.api(MethodGet,
+             "/eth/v1/debug/beacon/heads") do () -> RestApiResponse:
+    return RestApiResponse.jsonResponse(
+      node.dag.heads.mapIt((root: it.root, slot: it.slot))
+    )
+
   # https://ethereum.github.io/beacon-APIs/#/Debug/getDebugChainHeadsV2
   router.api(MethodGet,
              "/eth/v2/debug/beacon/heads") do () -> RestApiResponse:

beacon_chain/spec/eth2_apis/rest_debug_calls.nim

@@ -13,6 +13,11 @@ import
 
 export chronos, client, rest_types, eth2_rest_serialization
 
+proc getDebugChainHeads*(): RestResponse[GetDebugChainHeadsResponse] {.
+     rest, endpoint: "/eth/v1/debug/beacon/heads",
+     meth: MethodGet.}
+  ## https://ethereum.github.io/beacon-APIs/#/Beacon/getDebugChainHeads
+
 proc getStateV2Plain*(state_id: StateIdent): RestPlainResponse {.
      rest, endpoint: "/eth/v2/debug/beacon/states/{state_id}",
      accept: preferSSZ,

docs/the_nimbus_book/src/api.md

@@ -466,6 +466,14 @@ Equivalent call in the official REST API:
 curl http://localhost:5052/eth/v2/debug/beacon/states/head -s | jq
 ```
 
+### [`get_v1_debug_beacon_heads`](https://ethereum.github.io/eth2.0-APIs/#/Debug/getDebugChainHeads)
+
+Equivalent call in the official REST API:
+
+```
+curl http://localhost:5052/eth/v1/debug/beacon/heads -s | jq
+```
+
 ## Nimbus extensions
 
 ### getBeaconHead

ncli/resttest-rules.json

@@ -2817,6 +2817,18 @@
       "body": [{"operator": "jstructcmps", "start": ["data"], "value": {"chain_id": "", "address": ""}}]
     }
   },
+  {
+    "topics": ["debug"],
+    "request": {
+      "url": "/eth/v1/debug/beacon/heads",
+      "headers": {"Accept": "application/json"}
+    },
+    "response": {
+      "status": {"operator": "equals", "value": "200"},
+      "headers": [{"key": "Content-Type", "value": "application/json", "operator": "equals"}],
+      "body": [{"operator": "jstructcmps", "start": ["data"], "value": [{"root": "", "slot": ""}]}]
+    }
+  },
   {
     "topics": ["debug", "beacon_states_head_slow", "slow"],
     "request": {