Update integration docs to include OpenMetrics V2

[yzhan289]

What does this PR do?

This PR adds a new section for OpenMetricsV2. This also adds the IBM i architecture page in the navigation bar, since it was not included.

Motivation

Updating Istio documentation in #10304 and needed to link to a source of truth.

Additional Notes

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• PR title must be written as a CHANGELOG entry (see why)
• Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
• PR must have changelog/ and integration/ labels attached

[ofek]

Since this seems to be an incomplete copy+paste from the RFC, it doesn't fit the context in which it now inhabits. Let's:

1. Make a new directory docs/developer/legacy and move prometheus.md there. Do not include this in the nav section of mkdocs.yml.
2. Rename openmetricsv2.md to openmetrics.md.
3. Write it from scratch to simply reflect the current state of things like we're doing for Open Metrics configs. See https://datadoghq.dev/integrations-core/base/databases/ for an example. The target audience is a person (likely teammate) implementing an Open Metrics-based check.
4. Link to ../legacy/prometheus.md at some point.

[jtappa]

Just some small feedback, mostly on styling for our processes.

[codecov]

Codecov Report

Merging #10500 (fe87c1c) into master (eca1321) will increase coverage by 0.02%.
The diff coverage is n/a.

Flag	Coverage Δ
active_directory	100.00% <ø> (ø)
activemq_xml	82.31% <ø> (ø)
aerospike	86.97% <ø> (+0.36%)	⬆️
airflow	90.00% <ø> (ø)
amazon_msk	88.83% <ø> (ø)
ambari	85.75% <ø> (ø)
apache	95.08% <ø> (ø)
aspdotnet	93.87% <ø> (ø)
avi_vantage	91.92% <ø> (ø)
azure_iot_edge	82.01% <ø> (ø)
btrfs	82.91% <ø> (ø)
cacti	83.95% <ø> (ø)
cassandra_nodetool	94.19% <ø> (ø)
ceph	91.02% <ø> (ø)
cilium	85.84% <ø> (+1.88%)	⬆️
cisco_aci	95.88% <ø> (+0.03%)	⬆️
citrix_hypervisor	87.50% <ø> (ø)
clickhouse	95.63% <ø> (ø)
cloud_foundry_api	95.98% <ø> (+0.12%)	⬆️
cockroachdb	97.18% <ø> (ø)
consul	91.74% <ø> (ø)
coredns	95.74% <ø> (ø)
couch	95.19% <ø> (+0.24%)	⬆️
couchbase	81.45% <ø> (ø)
crio	100.00% <ø> (ø)
datadog_checks_base	89.69% <ø> (+0.40%)	⬆️
datadog_checks_dev	79.69% <ø> (-0.05%)	⬇️
datadog_checks_downloader	80.64% <ø> (ø)
datadog_cluster_agent	97.50% <ø> (ø)
directory	94.87% <ø> (ø)
disk	91.13% <ø> (-0.49%)	⬇️
dns_check	94.00% <ø> (ø)
dotnetclr	100.00% <ø> (ø)
druid	97.70% <ø> (ø)
ecs_fargate	76.15% <ø> (+1.97%)	⬆️
eks_fargate	94.05% <ø> (ø)
elastic	88.65% <ø> (ø)
etcd	93.27% <ø> (ø)
exchange_server	100.00% <ø> (ø)
external_dns	100.00% <ø> (ø)
fluentd	94.77% <ø> (ø)
gearmand	77.27% <ø> (+1.29%)	⬆️
gitlab	89.94% <ø> (ø)
gitlab_runner	91.94% <ø> (ø)
glusterfs	80.09% <ø> (+0.92%)	⬆️
go_expvar	92.49% <ø> (ø)
gunicorn	93.60% <ø> (ø)
haproxy	95.08% <ø> (+0.16%)	⬆️
harbor	81.29% <ø> (ø)
hazelcast	92.39% <ø> (ø)
hdfs_datanode	89.30% <ø> (ø)
hdfs_namenode	87.01% <ø> (ø)
http_check	89.98% <ø> (+1.76%)	⬆️
ibm_db2	94.84% <ø> (ø)
ibm_i	80.65% <ø> (ø)
ibm_mq	89.45% <ø> (ø)
ibm_was	97.45% <ø> (ø)
iis	93.01% <ø> (ø)
istio	77.67% <ø> (+0.59%)	⬆️
kafka_consumer	82.28% <ø> (ø)
kong	92.21% <ø> (ø)
kube_apiserver_metrics	97.35% <ø> (ø)
kube_controller_manager	96.85% <ø> (ø)
kube_dns	98.85% <ø> (ø)
kube_metrics_server	100.00% <ø> (ø)
kube_proxy	100.00% <ø> (ø)
kube_scheduler	96.20% <ø> (ø)
kubelet	89.61% <ø> (ø)
kubernetes_state	89.52% <ø> (-0.16%)	⬇️
kyototycoon	85.96% <ø> (ø)
lighttpd	83.64% <ø> (ø)
linkerd	85.14% <ø> (+1.14%)	⬆️
linux_proc_extras	96.22% <ø> (ø)
mapr	82.62% <ø> (ø)
mapreduce	81.30% <ø> (ø)
marathon	83.12% <ø> (ø)
marklogic	95.33% <ø> (ø)
mcache	93.52% <ø> (ø)
mesos_master	90.68% <ø> (ø)
mesos_slave	93.63% <ø> (ø)
mongo	94.31% <ø> (+0.28%)	⬆️
mysql	86.40% <ø> (+0.09%)	⬆️
nagios	89.53% <ø> (ø)
network	77.76% <ø> (+1.00%)	⬆️
nfsstat	95.20% <ø> (ø)
nginx	94.62% <ø> (+0.86%)	⬆️
nginx_ingress_controller	98.30% <ø> (ø)
openldap	96.33% <ø> (ø)
openmetrics	97.14% <ø> (ø)
openstack	51.30% <ø> (ø)
openstack_controller	90.74% <ø> (ø)
oracle	93.65% <ø> (+0.52%)	⬆️
pdh_check	95.65% <ø> (ø)
pgbouncer	90.45% <ø> (ø)
php_fpm	90.04% <ø> (+0.43%)	⬆️
postfix	88.04% <ø> (ø)
postgres	91.61% <ø> (+0.34%)	⬆️
powerdns_recursor	96.65% <ø> (ø)
process	85.07% <ø> (ø)
prometheus	94.17% <ø> (ø)
proxysql	98.97% <ø> (ø)
rabbitmq	94.40% <ø> (ø)
redisdb	86.96% <ø> (ø)
rethinkdb	97.93% <ø> (ø)
riak	99.22% <ø> (ø)
riakcs	93.61% <ø> (ø)
sap_hana	93.01% <ø> (ø)
scylla	100.00% <ø> (ø)
singlestore	90.81% <ø> (ø)
snmp	90.56% <ø> (+0.04%)	⬆️
snowflake	93.48% <ø> (ø)
sonarqube	95.69% <ø> (ø)
spark	93.41% <ø> (ø)
sqlserver	84.30% <ø> (+0.02%)	⬆️
squid	100.00% <ø> (ø)
ssh_check	91.58% <ø> (ø)
statsd	84.21% <ø> (+1.05%)	⬆️
supervisord	92.30% <ø> (ø)
system_core	91.04% <ø> (ø)
system_swap	98.30% <ø> (ø)
tcp_check	88.83% <ø> (ø)
teamcity	80.00% <ø> (ø)
tls	97.04% <ø> (+0.87%)	⬆️
tokumx	58.40% <ø> (?)
twemproxy	78.33% <ø> (ø)
twistlock	80.25% <ø> (ø)
varnish	84.57% <ø> (+0.24%)	⬆️
vault	95.00% <ø> (+0.55%)	⬆️
vertica	92.33% <ø> (ø)
voltdb	96.81% <ø> (ø)
vsphere	89.78% <ø> (+0.08%)	⬆️
win32_event_log	86.03% <ø> (+0.28%)	⬆️
windows_service	95.83% <ø> (ø)
wmi_check	92.91% <ø> (ø)
yarn	89.85% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

[djmitche]

🎉 docs 🎉