Add setdefault option to tcl module (#14686)

This commit introduces the command

spack module tcl setdefault <package>

similar to the one already available for lmod

Co-authored-by: Massimiliano Culpo <massimiliano.culpo@gmail.com>

share/spack/spack-completion.bash

@@ -1382,7 +1382,7 @@ _spack_module_tcl() {
     then
         SPACK_COMPREPLY="-h --help -n --name"
     else
-        SPACK_COMPREPLY="refresh find rm loads"
+        SPACK_COMPREPLY="refresh find rm loads setdefault"
     fi
 }
 
@@ -1422,6 +1422,15 @@ _spack_module_tcl_loads() {
     fi
 }
 
+_spack_module_tcl_setdefault() {
+    if $list_options
+    then
+        SPACK_COMPREPLY="-h --help"
+    else
+        _installed_packages
+    fi
+}
+
 _spack_monitor() {
     SPACK_COMPREPLY="-h --help --monitor --monitor-save-local --monitor-no-auth --monitor-tags --monitor-keep-going --monitor-host --monitor-prefix"
 }