Add SSE to userlog

[kobergj]

Alternate approach to #5286

Adds sse (Server-Sent Events) functionality to userlog

How to test sse functionality:

• start ocis from this branch
• connect to sse endpoint

curl --insecure -X GET -v -u einstein:relativity https://localhost:9200/ocs/v2.php/apps/notifications/api/v1/notifications/sse

• share something with einstein or invite him to a space
• see sse notification (also you will still get notification via web)
• changing language will affect future notifications without reconnecting to sse endpoint

[update-docs]

Thanks for opening this pull request! The maintainers of this repository would appreciate it if you would create a changelog item based on your changes.

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
1 Code Smell

28.9% Coverage
0.0% Duplication

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

43.6% Coverage
0.0% Duplication