Add basic telemetry features

[julian-risch]

Proposed changes:

• This PR adds basic telemetry features. It allows sending anonymous usage statistics to steer the development process and support continuous software improvements for all of Haystack's users.
• A PR for updating the documentation on the Website is here: add telemetry documentation page haystack-website#268

The events contain an anonymous user id, which is a randomly generated uuid. There is no way to infer your identity from the user id or any other content of the event.

To prevent revealing a user's identity, the following properties will never be used by telemetry:

• IP addresses
• Host names
• File paths
• Queries
• Document contents

You can have a look at the meta data that is shared about your setup by calling print_telemetry_report() from haystack/telemetry.py. If you would like to inspect all information that telemetry shares when you use Haystack, you can enable writing all events to a log file by calling enable_writing_events_to_file(). The default location of that file is ~/.haystack/telemetry.log.

Here is an exemplary event that is sent when tutorial 1 is executed via running Tutorial1_Basic_QA_Pipeline.py.

{
    "event": "tutorial 1 executed",
    "distinct_id": "9baab867-3bc8-438c-9974-a192c9d53cd1",
    "properties": {
        "os_family": "Darwin",
        "os_machine": "arm64",
        "os_version": "21.3.0",
        "haystack_version": "1.0.0",
        "python_version": "3.9.6",
        "torch_version": "1.9.0",
        "transformers_version": "4.13.0"
        "execution_env": "script",
        "context": null,
        "n_gpu": 0,
    },
}

Users can opt-out of telemetry via the following options.

• disable telemetry by calling disable_telemetry() within Python or by setting the environment variable HAYSTACK_TELEMETRY_ENABLED to "False" directly
• if using a bash shell, by adding the following line to the file ~/.bashrc to permanently disable telemetry: export HAYSTACK_TELEMETRY_ENABLED=False.
• if using zsh, e.g., on MacOS, by adding that line to the file ~/.zshrc.
• if using the standard command prompt in Windows, by setting a user-level environment variable via running the following command to permanently disable telemetry: setx HAYSTACK_TELEMETRY_ENABLED "False".
• if using the Windows PowerShell the command is: [Environment]::SetEnvironmentVariable("HAYSTACK_TELEMETRY_ENABLED","False","User").

To Do

• The posthog server needs to be changed from the development server to the production server.
• The public Haystack demo needs to set the context variable.
• Change the link to the documentation page about telemetry.
• Make sure the CI does not generate events. All events sent by CI can now be filtered out via execution_env != "ci".
• Make sure running api and ui tests locally does not generate events

Status (please check what you already did):

• First draft (up for discussions & feedback)
• Final code
• Added tests
• Updated documentation -> add telemetry documentation page haystack-website#268

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[ZanSara]

Looks good! I added many comments but most are minor and a few are simply architectural. There's only one related to model_name_or_path that might be worth looking into, and some concerns of mine about the generous use of except Exception: pass. Nothing blocking though 🙂

[ZanSara]

Looks good 🙂 As soon as the tests pass it can be merged. Good job! 👍

[tstadel]

Looks good!
I'd however get rid of the Thread in fire_and_forget as posthog already takes care of this and creating threads is a rather expensive operation (can take several 10s or 100s of ms). Note that currently we create and destroy a thread on any call.