Add the ability to assert the external_tags when running tests

[FlorentClarret]

What does this PR do?

Add the ability to assert the external_tags when running tests

Motivation

The Platform integrations team uses them and would like to have a way to assert them without mocking the function.

Additional Notes

• I'll update the ambari tests to use this to avoid issues with the changelog in another PR
• Relates to https://datadoghq.atlassian.net/browse/AITS-287

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Changelog entries must be created for modifications to shipped code
• Add the qa/skip-qa label if the PR doesn't need to be tested during QA.

[codecov]

Codecov Report

Merging #16089 (b9b09f9) into master (62653d5) will increase coverage by 0.05%.
Report is 4 commits behind head on master.
The diff coverage is 89.18%.

Flag	Coverage Δ
activemq	?
aerospike	87.17% <ø> (+0.32%)	⬆️
airflow	89.57% <ø> (ø)
cassandra	?
cassandra_nodetool	93.16% <ø> (ø)
ceph	91.07% <ø> (ø)
cilium	77.72% <ø> (+0.87%)	⬆️
clickhouse	95.65% <ø> (ø)
cockroachdb	91.52% <ø> (ø)
confluent_platform	81.96% <ø> (?)
consul	91.65% <ø> (ø)
couch	95.43% <ø> (+0.24%)	⬆️
couchbase	84.28% <ø> (ø)
datadog_checks_base	89.66% <89.18%> (+0.36%)	⬆️
datadog_checks_dev	79.93% <ø> (-2.49%)	⬇️
disk	85.20% <ø> (-6.16%)	⬇️
dns_check	93.90% <ø> (ø)
dotnetclr	91.39% <ø> (+12.90%)	⬆️
elastic	93.36% <ø> (ø)
envoy	95.09% <ø> (+0.41%)	⬆️
etcd	95.56% <ø> (ø)
exchange_server	96.85% <ø> (+11.81%)	⬆️
fluentd	94.77% <ø> (ø)
gearmand	78.26% <ø> (+1.24%)	⬆️
gitlab	92.10% <ø> (+1.21%)	⬆️
gitlab_runner	91.94% <ø> (ø)
glusterfs	80.09% <ø> (+0.90%)	⬆️
haproxy	95.13% <ø> (+0.16%)	⬆️
harbor	89.68% <ø> (ø)
hdfs_datanode	89.74% <ø> (ø)
hdfs_namenode	86.72% <ø> (ø)
hive	?
hivemq	?
hudi	73.91% <ø> (?)
ibm_ace	91.89% <ø> (ø)
ibm_db2	95.35% <ø> (ø)
ibm_mq	91.26% <ø> (-0.14%)	⬇️
ibm_was	96.08% <ø> (ø)
ignite	?
iis	95.05% <ø> (ø)
istio	77.74% <ø> (+0.52%)	⬆️
jboss_wildfly	?
kafka	?
kafka_consumer	93.23% <ø> (ø)
kong	87.56% <ø> (ø)
lighttpd	83.64% <ø> (ø)
linkerd	85.14% <ø> (+1.14%)	⬆️
mapreduce	81.81% <ø> (ø)
marklogic	96.51% <ø> (ø)
mesos_master	89.75% <ø> (ø)
mesos_slave	93.63% <ø> (ø)
mongo	95.94% <ø> (ø)
mysql	87.46% <ø> (+0.03%)	⬆️
nginx	95.24% <ø> (+0.54%)	⬆️
openldap	96.79% <ø> (ø)
oracle	88.63% <ø> (ø)
pdh_check	97.82% <ø> (ø)
postgres	91.94% <ø> (+<0.01%)	⬆️
powerdns_recursor	96.65% <ø> (ø)
presto	?
proxysql	98.97% <ø> (ø)
rabbitmq	96.04% <ø> (ø)
ray	96.45% <ø> (ø)
redisdb	87.78% <ø> (ø)
rethinkdb	97.93% <ø> (ø)
riakcs	93.61% <ø> (ø)
sap_hana	91.37% <ø> (ø)
scylla	99.49% <ø> (ø)
snmp	47.13% <ø> (+0.02%)	⬆️
solr	?
sonarqube	98.24% <ø> (ø)
spark	93.63% <ø> (ø)
sqlserver	87.54% <ø> (+0.06%)	⬆️
squid	100.00% <ø> (ø)
ssh_check	91.58% <ø> (ø)
tcp_check	90.23% <ø> (-2.70%)	⬇️
teamcity	88.74% <ø> (+3.21%)	⬆️
tomcat	?
varnish	84.39% <ø> (+0.26%)	⬆️
vault	95.53% <ø> (+0.57%)	⬆️
vertica	98.34% <ø> (ø)
voltdb	96.85% <ø> (ø)
vsphere	95.77% <ø> (+0.04%)	⬆️
weblogic	71.73% <ø> (ø)
windows_performance_counters	98.36% <ø> (ø)
windows_service	94.75% <ø> (+0.55%)	⬆️
yarn	89.59% <ø> (ø)
zk	83.08% <ø> (+1.30%)	⬆️

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[github-actions]

Test Results

     998 files       998 suites   7h 35m 56s ⏱️
  6 135 tests   6 066 ✔️      69 💤 0 ❌
26 147 runs  21 751 ✔️ 4 396 💤 0 ❌

Results for commit b9b09f9.

♻️ This comment has been updated with latest results.