module_file_support: update format for configuration (#27598)

lib/spack/docs/module_file_support.rst

@@ -273,6 +273,7 @@ of the installed software. For instance, in the snippet below:
 .. code-block:: yaml
 
    modules:
+     default:
        tcl:
          # The keyword `all` selects every package
          all:
@@ -322,6 +323,7 @@ your system. If you write a configuration file like:
 .. code-block:: yaml
 
    modules:
+     default:
        tcl:
          whitelist: ['gcc', 'llvm']  # Whitelist will have precedence over blacklist
          blacklist: ['%gcc@4.4.7']   # Assuming gcc@4.4.7 is the system compiler
@@ -349,6 +351,7 @@ shows how to set hash length in the module file names:
 .. code-block:: yaml
 
    modules:
+     default:
        tcl:
          hash_length: 7
 
@@ -360,6 +363,7 @@ For instance, the following config options,
 .. code-block:: yaml
 
    modules:
+     default:
        tcl:
          all:
            suffixes:
@@ -379,6 +383,7 @@ covered in :ref:`adding_projections_to_views`.
 .. code-block:: yaml
 
   modules:
+    default:
       tcl:
         projections:
           all: '{name}/{version}-{compiler.name}-{compiler.version}-module'
@@ -403,6 +408,7 @@ that are already in the LMod hierarchy.
      .. code-block:: yaml
 
         modules:
+          default:
             enable:
               - tcl
             tcl:
@@ -431,6 +437,7 @@ that are already in the LMod hierarchy.
      .. code-block:: yaml
 
        modules:
+         default:
            enable:
              - lmod
            lmod:
@@ -591,6 +598,7 @@ do so by using the environment blacklist:
 .. code-block:: yaml
 
    modules:
+     default:
        tcl:
          all:
            filter:
@@ -614,6 +622,7 @@ activated using ``spack activate``:
 .. code-block:: yaml
 
    modules:
+     default:
        tcl:
          ^python:
            autoload: 'direct'
@@ -633,6 +642,7 @@ The allowed values for the ``autoload`` statement are either ``none``,
   .. code-block:: yaml
 
      modules:
+       default:
          lmod:
            all:
              autoload: 'direct'