MM-55060 - Add PushSubTypeCalls for calls-specific push notifications

[cpoile]

Summary

• This is the second PR to support calls-specific push notifications.

• We are now sending a sub_type and keeping type as message. This allows us to support old push proxies, new push proxies, old servers, new servers, and old mobile clients and new mobile clients.

• Previous PR: MM-55060 - Calls: Add PushTypeCalls for calls-specific push notifications #561

• see also:

• MM-55060 - Calls: Add PushTypeCalls for calls-specific push notifications mattermost#25405

• MM-55060 - Calls: Add PushTypeCalls for calls-specific push notifications mattermost-push-proxy#110

• MM-55036 - Calls: Fix: Receiving in-app notifications for calls notifications while active mattermost-mobile#7623

• NOTE: will need to update the MM server dependency once that PR is merged.

Ticket Link

• https://mattermost.atlassian.net/browse/MM-55060

[codecov-commenter]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (47cd7a7) 6.10% compared to head (6cc3af7) 5.77%.

Files	Patch %	Lines
server/push_notifications.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##            main    #564      +/-   ##
========================================
- Coverage   6.10%   5.77%   -0.34%     
========================================
  Files         24      24              
  Lines       4602    4558      -44     
========================================
- Hits         281     263      -18     
+ Misses      4300    4277      -23     
+ Partials      21      18       -3     

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[cpoile]

For more explanation, see: mattermost/mattermost#25405 (comment)

[streamer45]

Are we keeping NewClient out of affection? :p

[cpoile]

so cruel :)

[streamer45]

It just wasn't meant to be :(

[cpoile]

For the record -- we're not changing our webapp-side dependency on the MM server code, so I elected not to upgrade the mattermost-webapp dependency. I want to reduce complication and churn and only update webapp when we need to.