feat: support variables in path towards the file to load as well

It is now possible to run:
< {{HOME}}/my_json_file

lua/rest-nvim/request/init.lua

@@ -19,15 +19,15 @@ local function get_importfile_name(bufnr, start_line, stop_line)
     local fileimport_string
     local fileimport_line
     fileimport_line = vim.api.nvim_buf_get_lines(bufnr, import_line - 1, import_line, false)
-    fileimport_string =
-      string.gsub(fileimport_line[1], "<", "", 1):gsub("^%s+", ""):gsub("%s+$", "")
-    -- local fileimport_path = path:new(fileimport_string)
-    -- if fileimport_path:is_absolute() then
-    if path:new(fileimport_string):is_absolute() then
-      return fileimport_string
+    fileimport_string = string.gsub(fileimport_line[1], "<", "", 1)
+      :gsub("^%s+", "")
+      :gsub("%s+$", "")
+	fileimport_spliced = utils.replace_vars(fileimport_string)
+    if path:new(fileimport_spliced):is_absolute() then
+      return fileimport_spliced
     else
       local file_dirname = vim.fn.expand("%:p:h")
-      local file_name = path:new(path:new(file_dirname), fileimport_string)
+      local file_name = path:new(path:new(file_dirname), fileimport_spliced)
       return file_name:absolute()
     end
   end