feat: query earliest attestation nonce (#2724)

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## Overview

So that the orchestartor is able to query the earliest attestation nonce
and sign up to it.

This change is not breaking and is just adding a new API endpoint.

PS: I originally thought that this was already implemented. But sadly,
we didn't.

## Checklist

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- [ ] New and updated code has appropriate documentation
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---------

Co-authored-by: Rootul P <[email protected]>
(cherry picked from commit a3e1da0)

# Conflicts:
#	x/qgb/types/query.pb.go

app/test/qgb_rpc_test.go

@@ -50,6 +50,16 @@ func TestQGBRPCQueries(t *testing.T) {
 				return err
 			},
 		},
+		{
+			name: "earliest attestation nonce",
+			req: func() error {
+				_, err := queryClient.EarliestAttestationNonce(
+					context.Background(),
+					&types.QueryEarliestAttestationNonceRequest{},
+				)
+				return err
+			},
+		},
 		{
 			name: "data commitment range for height",
 			req: func() error {

proto/celestia/qgb/v1/query.proto

@@ -31,6 +31,11 @@ service Query {
       returns (QueryLatestAttestationNonceResponse) {
     option (google.api.http).get = "/qgb/v1/attestations/nonce/latest";
   }
+  // EarliestAttestationNonce queries the earliest attestation nonce.
+  rpc EarliestAttestationNonce(QueryEarliestAttestationNonceRequest)
+      returns (QueryEarliestAttestationNonceResponse) {
+    option (google.api.http).get = "/qgb/v1/attestations/nonce/earliest";
+  }
   // LatestValsetRequestBeforeNonce Queries latest Valset request before nonce.
   // And, even if the current nonce is a valset, it will return the previous
   // one.
@@ -93,6 +98,11 @@ message QueryLatestAttestationNonceRequest {}
 // QueryLatestAttestationNonceResponse latest attestation nonce response
 message QueryLatestAttestationNonceResponse { uint64 nonce = 1; }
 
+// QueryEarliestAttestationNonceRequest earliest attestation nonce request
+message QueryEarliestAttestationNonceRequest {}
+// QueryEarliestAttestationNonceResponse earliest attestation nonce response
+message QueryEarliestAttestationNonceResponse { uint64 nonce = 1; }
+
 // QueryLatestValsetRequestBeforeNonceRequest latest Valset request before
 // universal nonce request
 message QueryLatestValsetRequestBeforeNonceRequest { uint64 nonce = 1; }

x/qgb/keeper/query_general.go

@@ -17,6 +17,16 @@ func (k Keeper) LatestUnbondingHeight(
 	}, nil
 }
 
+// EarliestAttestationNonce queries the earliest attestation nonce.
+func (k Keeper) EarliestAttestationNonce(
+	c context.Context,
+	_ *types.QueryEarliestAttestationNonceRequest,
+) (*types.QueryEarliestAttestationNonceResponse, error) {
+	return &types.QueryEarliestAttestationNonceResponse{
+		Nonce: k.GetEarliestAvailableAttestationNonce(sdk.UnwrapSDKContext(c)),
+	}, nil
+}
+
 func (k Keeper) Params(c context.Context, _ *types.QueryParamsRequest) (*types.QueryParamsResponse, error) {
 	params := k.GetParams(sdk.UnwrapSDKContext(c))
 	return &types.QueryParamsResponse{