[META 786] Do not use proxy when querying cloud metadata from APM agents

[elastic-apm-tech]

See meta issue for the description and details:

• Meta issue: Do not use proxy when querying cloud metadata from APM agents apm#786

[beniwohli]

It looks like we're already doing this, by coincidence. We create separate connection pools where we fetch the cloud metadata:

apm-agent-python/elasticapm/utils/cloud.py

Line 43 in d19c5ff

http = urllib3.PoolManager()

apm-agent-python/elasticapm/utils/cloud.py

Line 95 in d19c5ff

http = urllib3.PoolManager()

apm-agent-python/elasticapm/utils/cloud.py

Line 134 in d19c5ff

http = urllib3.PoolManager()

In contrast, the connection pool used in the transport explicitly sets up a ProxyManager if the HTTP[S]_PROXY environment variable is set.

apm-agent-python/elasticapm/transport/http.py

Lines 124 to 129 in d19c5ff

	proxies = getproxies_environment()
	proxy_url = proxies.get("https", proxies.get("http", None))
	if proxy_url and not proxy_bypass_environment(url_parts.netloc):
	self._http = urllib3.ProxyManager(proxy_url, **self._pool_kwargs)
	else:
	self._http = urllib3.PoolManager(**self._pool_kwargs)

@basepi agree to close this as completed? Or should we add comments in utils/cloud.py to not use ProxyManager there, just in case?