I managed to do it!!!.
If you wanna make your own subject (title) with particular labels you
should use {{ .GroupLabels.your_label }} and put it in this row:
{{ define "__subject" }}[{{ .Status | toUpper }}{{ if eq .Status "firing"
}}:{{ .Alerts.Firing | len }}{{ end }}] __put here___ {{ end }}
Now my notification looks like this:
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