Change "start" command to support automatically run migrations

We will need this for instance when doing CD and migrations from CI.

src/app/app.ml

@@ -3,6 +3,17 @@ module Sig = App_sig
 let ( let* ) = Lwt_result.bind
 
 module Make (Kernel : Sig.KERNEL) (App : Sig.APP) = struct
+  let start_cmd =
+    Cmd.make ~name:"start"
+      ~help:
+        "Run \"start <with_migration>\" to first run migrations and then start \
+         the web server"
+      ~description:"Start the Sihl app"
+      ~fn:(fun _ ->
+        let ctx = Core.Ctx.empty in
+        Kernel.WebServer.start_server ctx |> Lwt.map Result.ok)
+      ()
+
   let start_app () =
     (let ctx = Core.Ctx.empty in
      Log.debug (fun m -> m "APP: Register services");
@@ -13,7 +24,8 @@ module Make (Kernel : Sig.KERNEL) (App : Sig.APP) = struct
      Log.debug (fun m -> m "APP: Register routes");
      let* () = Kernel.WebServer.register_routes ctx App.routes in
      Log.debug (fun m -> m "APP: Register commands");
-     let* () = Kernel.Cmd.register_commands ctx App.commands in
+     let commands = List.cons start_cmd App.commands in
+     let* () = Kernel.Cmd.register_commands ctx commands in
      Log.debug (fun m -> m "APP: Register schedules");
      let _ = App.schedules |> List.map (Kernel.Schedule.schedule ctx) in
      Log.debug (fun m -> m "APP: Start services");

src/web/web_server_service.ml

@@ -22,14 +22,7 @@ module Make (CmdService : Cmd.Sig.SERVICE) : Web_server_sig.SERVICE = struct
     let _ = Opium.Std.App.start app in
     run_forever ()
 
-  let start_cmd =
-    Cmd.make ~name:"start" ~description:"Starts the web server"
-      ~fn:(fun _ ->
-        let ctx = Core.Ctx.empty in
-        start_server ctx |> Lwt.map Result.return)
-      ()
-
-  let on_init ctx = CmdService.register_command ctx start_cmd
+  let on_init _ = Lwt_result.return ()
 
   let on_start _ = Lwt_result.return ()
 

src/web/web_server_sig.ml

@@ -1,6 +1,8 @@
 module type SERVICE = sig
   include Core_container.SERVICE
 
+  val start_server : Core.Ctx.t -> unit Lwt.t
+
   val register_routes :
     Core_ctx.t ->
     Web_server_core.stacked_routes ->

src/web/web_utils.ml

@@ -1,6 +1,6 @@
 open Base
 
-let externalize ?(prefix = Config.read_string_default ~default:"" "URL_PREFIX")
+let externalize ?(prefix = Config.read_string_default ~default:"" "PREFIX_PATH")
     path =
   path |> String.split ~on:'/' |> List.cons prefix |> String.concat ~sep:"/"
   |> String.substr_replace_all ~pattern:"//" ~with_:"/"