server: add db and table grants apis by id routes

This commit introduces apis to retrieve db and table
level grants.
The following GET routes have been introduced to api/v2:
- `api/v2/grants/databases/:database_id`
- `api/v2/grants/tables/:table_id`

Both provide pagination capabilities via URL query params:
- pageSize: int
- pageNum: int

Epic: CRDB-37558
Part of: #131211

Release note: None

pkg/server/BUILD.bazel

@@ -8,6 +8,7 @@ go_library(
         "api_v2.go",
         "api_v2_constants.go",
         "api_v2_databases_metadata.go",
+        "api_v2_grants.go",
         "api_v2_ranges.go",
         "api_v2_sql.go",
         "api_v2_sql_schema.go",
@@ -425,6 +426,7 @@ go_test(
     size = "enormous",
     srcs = [
         "api_v2_databases_metadata_test.go",
+        "api_v2_grants_test.go",
         "api_v2_ranges_test.go",
         "api_v2_sql_schema_test.go",
         "api_v2_sql_test.go",

pkg/server/api_v2.go

@@ -51,6 +51,12 @@ import (
 	"github.com/gorilla/mux"
 )
 
+// Path variables.
+const (
+	dbIdPathVar    = "database_id"
+	tableIdPathVar = "table_id"
+)
+
 type ApiV2System interface {
 	health(w http.ResponseWriter, r *http.Request)
 	listNodes(w http.ResponseWriter, r *http.Request)
@@ -191,6 +197,8 @@ func registerRoutes(
 		{"table_metadata/", a.GetTableMetadata, true, authserver.RegularRole, true},
 		{"table_metadata/{table_id:[0-9]+}/", a.GetTableMetadataWithDetails, true, authserver.RegularRole, true},
 		{"table_metadata/updatejob/", a.TableMetadataJob, true, authserver.RegularRole, true},
+		{fmt.Sprintf("grants/databases/{%s:[0-9]+}/", dbIdPathVar), a.getDatabaseGrants, true, authserver.RegularRole, true},
+		{fmt.Sprintf("grants/tables/{%s:[0-9]+}/", tableIdPathVar), a.getTableGrants, true, authserver.RegularRole, true},
 	}
 
 	// For all routes requiring authentication, have the outer mux (a.mux)