feat(besadii): Tag gerrit comments as autogenerated

This is a bit of an under-documented feature, but if the "tag" field for
a gerrit review starts with the string
"autogenerated:<something>~<something-else>", only the last comment per
instance of <something> will be shown by default on the CL page (with
the rest viewable by toggling the "Show all entries" switch). The idea
behind the "<something-else>" tag is to be used for the "type" of
comment within a particular system - gerrit's documentation gives the
example of one tag for "the build is running" and another for "the build
has finished, here's the result".

Change-Id: I9199a6ed97beca1b3a51ec5d6230c6c8358ba2b3
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3374
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>

ops/besadii/main.go

@@ -221,6 +221,7 @@ type reviewInput struct {
 	Labels                         map[string]int `json:"labels"`
 	OmitDuplicateComments          bool           `json:"omit_duplicate_comments"`
 	IgnoreDefaultAttentionSetRules bool           `json:"ignore_default_attention_set_rules"`
+	Tag                            string         `json:"tag"`
 }
 
 func postCommandMain() {
@@ -267,6 +268,8 @@ func postCommandMain() {
 
 		// Update the attention set if we are failing this patchset.
 		IgnoreDefaultAttentionSetRules: verified == 1,
+
+		Tag: "autogenerated:buildkite~result",
 	}
 
 	body, _ := json.Marshal(review)