[MM-53015] Allow the user_agent field to be included in context

[kyeongsoosoo]

Summary

When the InvokeCall method is executed, AppContext is assigned an expanded context.

mattermost-plugin-apps/server/proxy/invoke_call.go

Lines 185 to 190 in 89a1e4c

	// expand
	expanded, err := p.expandContext(r, app, &creq.Context, creq.Expand, expandGetter)
	if err != nil {
	return nil, errors.Wrap(err, "failed to expand context")
	}
	creq.Context = *expanded

I found that the user_agent field disappears because expandContext method initializes the UserAgentContext when it runs.
I changed the user_agent and track_as_submit fields to keep their original values on initialization.

mattermost-plugin-apps/server/proxy/expand.go

Lines 216 to 217 in 89a1e4c

	// Cleanup fields that must not go to the app.
	e.Context.UserAgentContext = apps.UserAgentContext{}

Ticket Link

Fixes mattermost/mattermost#23621
JIRA https://mattermost.atlassian.net/browse/MM-53015

[mattermost-build]

Hello @kyeongsoosoo,

Thanks for your pull request! A Core Committer will review your pull request soon. For code contributions, you can learn more about the review process here.

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.03% 🎉

Comparison is base (89a1e4c) 20.12% compared to head (6a56b64) 20.16%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #480      +/-   ##
==========================================
+ Coverage   20.12%   20.16%   +0.03%     
==========================================
  Files          80       80              
  Lines        6609     6612       +3     
==========================================
+ Hits         1330     1333       +3     
  Misses       5147     5147              
  Partials      132      132              

Files Changed	Coverage Δ
server/proxy/expand.go	46.01% <100.00%> (+0.41%)	⬆️

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[kyeongsoosoo]

/update-branch

[mattermost-build]

This PR has been automatically labelled "stale" because it hasn't had recent activity.
A core team member will check in on the status of the PR to help with questions.
Thank you for your contribution!

[hanzei]

Thanks for the contribution and also for adding tests 👍