app: add metrics for logs retrieved in tail requests
app: add metrics for logs retrieved in tail requests

(cherry picked from commit 89fcf18a9d36103339a2df0e2860d41da1b493c6)

guilhermebr/tsuru,guilhermebr/tsuru,tsuru/tsuru,tsuru/tsuru,tsuru/tsuru,tsuru/tsuru,guilhermebr/tsuru,guilhermebr/tsuru