[loki microservices]: allow custom gateway server configuration (#6138)
[loki microservices]: allow custom gateway server configuration (#6138)

* feat(loki)!: allow custom server configuration

Signed-off-by: irizzant <fd7c71140f6b5272c367143a9a36d1b881319443@gmail.com>

* doc(loki): fix documentation

* refactor: move server_snippet under gateway.libsonnet

Signed-off-by: irizzant <fd7c71140f6b5272c367143a9a36d1b881319443@gmail.com>
grafana/loki,grafana/loki,grafana/loki,grafana/loki,grafana/loki,grafana/loki