chore: relocate some release files from data/ to rel/

data dir at the root is easily confused with the data
dir for EMQ X at run time

mix.exs

@@ -279,7 +279,7 @@ defmodule EMQXUmbrella.MixProject do
     )
 
     vars_rendered =
-      File.read!("data/emqx_vars")
+      File.read!("rel/emqx_vars")
       |> from_rebar_to_eex_template()
       |> EEx.eval_string(assigns)
 
@@ -338,7 +338,7 @@ defmodule EMQXUmbrella.MixProject do
     end
 
     built_on_rendered =
-      File.read!("data/BUILT_ON")
+      File.read!("rel/BUILT_ON")
       |> from_rebar_to_eex_template()
       |> EEx.eval_string(assigns)
 

rebar.config.erl

@@ -326,8 +326,8 @@ relx_overlay(ReleaseType, Edition) ->
     , {mkdir, "data/configs"}
     , {mkdir, "data/patches"}
     , {mkdir, "data/scripts"}
-    , {template, "data/emqx_vars", "releases/emqx_vars"}
-    , {template, "data/BUILT_ON", "releases/{{release_version}}/BUILT_ON"}
+    , {template, "rel/emqx_vars", "releases/emqx_vars"}
+    , {template, "rel/BUILT_ON", "releases/{{release_version}}/BUILT_ON"}
     , {copy, "bin/emqx", "bin/emqx"}
     , {copy, "bin/emqx_ctl", "bin/emqx_ctl"}
     , {copy, "bin/node_dump", "bin/node_dump"}