fix: allow users to extend their running workspace's deadline (#15895)

Fixes https://github.com/coder/coder/issues/15515

This change effectively reverts the changes introduced by
https://github.com/coder/coder/pull/13182 (for
https://github.com/coder/coder/issues/13078).

We also rename the `override-stop` command name to `extend` to match the
API endpoint's name (keeping an alias to allow `override-stop` to be used).

cli/testdata/coder_schedule_--help.golden

@@ -1,16 +1,15 @@
 coder v0.0.0-devel
 
 USAGE:
-  coder schedule { show | start | stop | override } <workspace>
+  coder schedule { show | start | stop | extend } <workspace>
 
   Schedule automated start and stop times for workspaces
 
 SUBCOMMANDS:
-    override-stop    Override the stop time of a currently running workspace
-                     instance.
-    show             Show workspace schedules
-    start            Edit workspace start schedule
-    stop             Edit workspace stop schedule
+    extend    Extend the stop time of a currently running workspace instance.
+    show      Show workspace schedules
+    start     Edit workspace start schedule
+    stop      Edit workspace stop schedule
 
 ———
 Run `coder --help` for a list of global options.

cli/testdata/coder_schedule_extend_--help.golden

@@ -1,15 +1,17 @@
 coder v0.0.0-devel
 
 USAGE:
-  coder schedule override-stop <workspace-name> <duration from now>
+  coder schedule extend <workspace-name> <duration from now>
 
-  Override the stop time of a currently running workspace instance.
+  Extend the stop time of a currently running workspace instance.
+
+  Aliases: override-stop
 
       * The new stop time is calculated from *now*.
     * The new stop time must be at least 30 minutes in the future.
     * The workspace template may restrict the maximum workspace runtime.
   
-   $ coder schedule override-stop my-workspace 90m
+   $ coder schedule extend my-workspace 90m
 
 ———
 Run `coder --help` for a list of global options.