Put completions in their own module (#4880)

docs/sample_config/default_config.nu

@@ -54,6 +54,7 @@ let-env NU_PLUGIN_DIRS = [
     ($nu.config-path | path dirname | path join 'plugins')
 ]
 
+module completions {
   # Custom completions for external commands (those outside of Nushell)
   # Each completions has two parts: the form of the external command, including its flags and parameters
   # and a helper command that knows how to complete values for those flags and parameters
@@ -67,7 +68,7 @@ def "nu-complete git remotes" [] {
     ^git remote | lines | each { |line| $line | str trim }
   }
 
-extern "git checkout" [
+  export extern "git checkout" [
     branch?: string@"nu-complete git branches" # name of the branch to checkout
     -b: string                                 # create and checkout a new branch
     -B: string                                 # create/reset and checkout a branch
@@ -92,7 +93,7 @@ extern "git checkout" [
     --pathspec-from-file: string               # read pathspec from file
   ]
 
-extern "git push" [
+  export extern "git push" [
     remote?: string@"nu-complete git remotes", # the name of the remote
     refspec?: string@"nu-complete git branches"# the branch / refspec
     --verbose(-v)                              # be more verbose
@@ -121,6 +122,10 @@ extern "git push" [
     --ipv4(-4)                                 # use IPv4 addresses only
     --ipv6(-6)                                 # use IPv6 addresses only
   ]
+}
+
+# Get just the extern definitions without the custom completion commands
+use completions *
 
 # for more information on themes see
 # https://github.com/nushell/nushell/blob/main/docs/How_To_Coloring_and_Theming.md