templates: add autotemplate for gemma3 (#9880)

This change allows the gemma3 template to be autodetected during `ollama
create`.

template/gemma3-instruct.gotmpl

@@ -0,0 +1,13 @@
+{{- range $i, $_ := .Messages }}
+{{- $last := eq (len (slice $.Messages $i)) 1 }}
+{{- if eq .Role "user" }}<start_of_turn>user
+{{- if and (eq $i 1) $.System }}
+{{ $.System }}
+{{ end }}
+{{ .Content }}<end_of_turn>
+{{ else if eq .Role "assistant" }}<start_of_turn>model
+{{ .Content }}<end_of_turn>
+{{ end }}
+{{- if $last }}<start_of_turn>model
+{{ end }}
+{{- end }}