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
 
 |      |                           |

docs/platforms/jfrog.md

@@ -62,10 +62,10 @@ provider "artifactory" {
 }
 ```
 
-When pushing the template, you can pass in the variables using the `--variable` flag:
+When pushing the template, you can pass in the variables using the `-V` flag:
 
 ```sh
-coder templates push --variable 'jfrog_url=https://YYY.jfrog.io' --variable 'artifactory_access_token=XXX'
+coder templates push --var 'jfrog_url=https://YYY.jfrog.io' --var 'artifactory_access_token=XXX'
 ```
 
 ## Installing jf