Sending an event adds tags from agent config

[christopherfrieler]

We have a host with the DataDog agent installed and its config present. When sending an event to DataDog with this Python library, the event gets the tags from the config file attached. In our case this leads to duplicate tags which breaks some event queries in DataDog.

I've seen that this library accesses an agent config if present to get the host name. And indeed, setting attach_host_name=False when sending the event prevents this behavior. However, I've found no hint in the documentation that there is more than the host name taken from the config file, nor could I retrace this in the code, yet.

Looks like a bug to me or at least the option attach_host_name is misleading.

To Reproduce

1. Have a host with a datadog agent installed and tags defined in its config file.
2. Send an event to Datadog using this library without disabling attach_host_name.
3. The event has the tags from the agent's config file (in addition to any other tags that were specified to event, even duplicate tags)

Expected behavior
Sending an event (directly via DataDogs http API) should not interfere with a DataDog agent installed on that host except in the documented way, i.e. getting the host name.

Versions
datadog: 0.45.0
Python: 3.8
OS: RHEL 8

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