EUI-2976: ExUI strategic solution

[paul-graham]

JIRA link (if applicable)

https://tools.hmcts.net/jira/browse/EUI-4128 ✅ DONE
https://tools.hmcts.net/jira/browse/EUI-4131 ✅ DONE
https://tools.hmcts.net/jira/browse/EUI-4135 ✅ DONE
https://tools.hmcts.net/jira/browse/EUI-4137 ✅ DONE
(All under https://tools.hmcts.net/jira/browse/EUI-2976)

Change description

Introduced socket.io to provide a mechanism for watching activity on a list of cases and indicating when a user is viewing or editing a given case. This mirrors the functionality already in the activity tracker but uses "sockets" (websockets or long polling, depending on the client configuration) and does away with the need for repeated polling.

Does this PR introduce a breaking change? (check one with "x")

[ ] Yes
[x] No, but I'd still suggest it should be a major release

[codecov]

Codecov Report

Merging #276 (442f9b1) into master (509d54c) will increase coverage by 12.62%.
The diff coverage is 93.47%.

❗ Current head 442f9b1 differs from pull request most recent head 3f19129. Consider uploading reports for the commit 3f19129 to get more accurate results

@@             Coverage Diff             @@
##           master     #276       +/-   ##
===========================================
+ Coverage   73.98%   86.60%   +12.62%     
===========================================
  Files          24       37       +13     
  Lines         419      672      +253     
===========================================
+ Hits          310      582      +272     
+ Misses        109       90       -19     

Impacted Files	Coverage Δ
app/security/cors.js	20.83% <0.00%> (-0.91%)	⬇️
server.js	0.00% <0.00%> (ø)
app/job/store-cleanup-job.js	35.00% <62.50%> (-3.47%)	⬇️
app/redis/instantiator.js	80.95% <80.95%> (ø)
app.js	76.08% <100.00%> (-0.51%)	⬇️
app/redis/redis-client.js	100.00% <100.00%> (+22.72%)	⬆️
app/routes/validate-request.js	100.00% <100.00%> (ø)
app/service/activity-service.js	100.00% <100.00%> (ø)
app/service/ttl-score-generator.js	100.00% <100.00%> (+50.00%)	⬆️
app/socket/index.js	100.00% <100.00%> (ø)
... and 12 more

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[udaydenduluri33]

In general all the parameters are missing the types. I will look at this PR once all the types are strongly typed. Thanks.

[paul-graham]

In general all the parameters are missing the types. I will look at this PR once all the types are strongly typed. Thanks.

This is a JavaScript project, not a TypeScript one. Therefore, no strong typing. 😁

[udaydenduluri33]

Approving on the basis that existing functionality is not touched
socket.io is introduced as an additional enhancement which could be feature toggled from application