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

Add the missing template property for addTags.

Fixes golang/vscode-go#965

Change-Id: I930e405f0dd1fe0267c8a321549dca49258e2772
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/273187
Trust: Suzy Mueller <suzmue@golang.org>
Run-TryBot: Suzy Mueller <suzmue@golang.org>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/273189
TryBot-Result: kokoro <noreply+kokoro@google.com>
diff --git a/package.json b/package.json
index db43bab..bf6c1ef 100644
--- a/package.json
+++ b/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,