feat(cli): add --var shorthand for --variable (#8710)

`--variable` is used frequently enough to deserve a shorthand. Unfortunately,
`-v` is taken by verbose, and `-V` is too easily confused with version or
verbose, so we're left with "--var".

docs/cli/templates_create.md

@@ -81,6 +81,14 @@ Disable the default behavior of granting template access to the 'everyone' group
 
 Specify a set of tags to target provisioner daemons.
 
+### --var
+
+|      |                           |
+| ---- | ------------------------- |
+| Type | <code>string-array</code> |
+
+Alias of --variable.
+
 ### --variable
 
 |      |                           |

docs/cli/templates_push.md

@@ -80,6 +80,14 @@ Specify a name for the new template version. It will be automatically generated
 
 Specify a set of tags to target provisioner daemons.
 
+### --var
+
+|      |                           |
+| ---- | ------------------------- |
+| Type | <code>string-array</code> |
+
+Alias of --variable.
+
 ### --variable
 
 |      |                           |