[FEATURE]Add distinct_id to group_identify

[sibinms]

Feature

• Add distinct_id to group_identify #137
• This PR adds the capability of passing distinct_id to the group_identify() function in the PostHog Client
• This allows the users to tag a group identify event to a person ID

Before

After

Sample code :

group_type = "business"
group_key = 2668  # business_id
distinct_id=2675  # user_id
ph_client = posthog.Client(api_key=POSTHOG_API_KEY)
ph_client.group_identify(group_type, group_key, properties, distinct_id=distinct_id)

[dmarticus]

Great work @sibinms! Can you please make the following changes so that this change is released immediately?

• update version.py to use 3.7.5 instead of 3.7.4
• add an entry to CHANGELOG.md for this version

Once that's done, I'll merge this and then run the workflow to deploy it to PyPi. Thanks for your contribution!

[dmarticus]

I fixed CI in master, so this is safe to merge and deploy. thanks again for the contribution!