[release] package.json: Add "template" property to go.addTags configuration

Add the missing template property for addTags.

Fixes #965

Change-Id: I930e405f0dd1fe0267c8a321549dca49258e2772
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/273187
Trust: Suzy Mueller <[email protected]>
Run-TryBot: Suzy Mueller <[email protected]>
Reviewed-by: Hyang-Ah Hana Kim <[email protected]>
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/273189
TryBot-Result: kokoro <[email protected]>

Author: suzmue

package.json

@@ -1697,6 +1697,11 @@
               ],
               "default": "snakecase",
               "description": "Transformation rule used by Go: Add Tags command to add tags"
+            },
+            "template": {
+              "type": "string",
+              "default": "",
+              "description": "Custom format used by Go: Add Tags command for the tag value to be applied"
             }
           },
           "additionalProperties": false,