The attribute max_alerts is not valid for webhook_configs for AlertManager version included in PMM v2.13.0

/usr/local/go/src/runtime/asm_amd64.s:1373. ^[[31mcomponent^[[0m=alertmanager
^[[36mINFO^[[0m[2021-01-12T10:03:11.846+00:00] STT is not enabled, doing nothing. ^[[36mcomponent^[[0m=checks
^[[31mERRO^[[0m[2021-01-12T10:03:12.620+00:00] Checking '/tmp/pmm-managed-config-alertmanager-122710806' FAILED: yaml: unmarshal errors:
 line 14: field max_alerts not found in type config.plain
amtool: error: failed to validate 1 file(s)
 ^[[31mcomponent^[[0m=alertmanager
^[[31mERRO^[[0m[2021-01-12T10:03:12.620+00:00] Failed to update configuration, will retry: exit status 1
Checking '/tmp/pmm-managed-config-alertmanager-122710806' FAILED: yaml: unmarshal errors:
 line 14: field max_alerts not found in type config.plain
amtool: error: failed to validate 1 file(s)

# docker create -v /srv --name pmm-data percona/pmm-server:2.13.0 /bin/true
7b73f35f3ccf2d4297b038a4ae10c88cb7c56e413a8264d30e99eba77eb1a241
# docker run -d -p 80:80 -p 443:443 --volumes-from pmm-data --name pmm-server --restart always percona/pmm-server:2.13.0
5f1ed1d08b88d8b79ba2239a27cecea70d89b3eaa98ee43acd7d2ea6fbfd2dcb

---
# You can edit this file; changes will be preserved.
route:
 receiver: webhook
 routes: []
receivers:
- name: 'webhook'
 webhook_configs:
 - url: 'http://127.0.0.1:5001/webhook'
- name: 'email'
 email_configs:
 - send_resolved: true # Send clear
 to: '[email protected]'
templates: []

# docker restart pmm-server
pmm-server
# docker exec -it pmm-server supervisorctl status
alertmanager RUNNING pid 25, uptime 0:00:05
clickhouse RUNNING pid 14, uptime 0:00:05
cron RUNNING pid 17, uptime 0:00:05
dashboard-upgrade EXITED Jan 12 10:02 AM
dbaas-controller STOPPED Not started
grafana RUNNING pid 15, uptime 0:00:05
nginx RUNNING pid 16, uptime 0:00:05
pmm-agent RUNNING pid 44, uptime 0:00:05
pmm-managed RUNNING pid 42, uptime 0:00:05
pmm-update-perform STOPPED Not started
postgresql RUNNING pid 13, uptime 0:00:05
prometheus STOPPED Not started
qan-api2 RUNNING pid 186, uptime 0:00:04
victoriametrics RUNNING pid 18, uptime 0:00:05
vmalert RUNNING pid 19, uptime 0:00:05

/usr/local/go/src/runtime/asm_amd64.s:1373. ^[[31mcomponent^[[0m=alertmanager
^[[36mINFO^[[0m[2021-01-12T10:03:11.846+00:00] STT is not enabled, doing nothing. ^[[36mcomponent^[[0m=checks
^[[31mERRO^[[0m[2021-01-12T10:03:12.620+00:00] Checking '/tmp/pmm-managed-config-alertmanager-122710806' FAILED: yaml: unmarshal errors:
 line 14: field max_alerts not found in type config.plain
amtool: error: failed to validate 1 file(s)
 ^[[31mcomponent^[[0m=alertmanager
^[[31mERRO^[[0m[2021-01-12T10:03:12.620+00:00] Failed to update configuration, will retry: exit status 1
Checking '/tmp/pmm-managed-config-alertmanager-122710806' FAILED: yaml: unmarshal errors:
 line 14: field max_alerts not found in type config.plain
amtool: error: failed to validate 1 file(s)

github.com/percona/pmm-managed/services/alertmanager.(*Service).validateConfig
 /home/builder/rpm/BUILD/pmm-managed-0db06f75cbb60d688e85a34133f51dd5d140fa25/src/github.com/percona/pmm-managed/services/alertmanager/alertmanager.go:281
github.com/percona/pmm-managed/services/alertmanager.(*Service).configAndReload
 /home/builder/rpm/BUILD/pmm-managed-0db06f75cbb60d688e85a34133f51dd5d140fa25/src/github.com/percona/pmm-managed/services/alertmanager/alertmanager.go:314
github.com/percona/pmm-managed/services/alertmanager.(*Service).updateConfiguration
 /home/builder/rpm/BUILD/pmm-managed-0db06f75cbb60d688e85a34133f51dd5d140fa25/src/github.com/percona/pmm-managed/services/alertmanager/alertmanager.go:194
github.com/percona/pmm-managed/services/alertmanager.(*Service).Run
 /home/builder/rpm/BUILD/pmm-managed-0db06f75cbb60d688e85a34133f51dd5d140fa25/src/github.com/percona/pmm-managed/services/alertmanager/alertmanager.go:162
main.main.func5
 /home/builder/rpm/BUILD/pmm-managed-0db06f75cbb60d688e85a34133f51dd5d140fa25/src/github.com/percona/pmm-managed/main.go:707
runtime.goexit
 /usr/local/go/src/runtime/asm_amd64.s:1373. ^[[31mcomponent^[[0m=alertmanager