Add thread support to slash commands

[d-gubert]

Apps will need to update their slash commands for them to send messages correctly aware of the thread.

Implementation provided by RocketChat/Rocket.Chat#15574

[codecov]

Codecov Report

Merging #164 into master will increase coverage by 0.09%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #164      +/-   ##
==========================================
+ Coverage   55.42%   55.51%   +0.09%     
==========================================
  Files          68       68              
  Lines        2396     2401       +5     
  Branches      360      360              
==========================================
+ Hits         1328     1333       +5     
  Misses       1068     1068

Impacted Files	Coverage Δ
src/server/managers/AppSlashCommandManager.ts	99.38% <100%> (ø)	⬆️
src/server/accessors/MessageBuilder.ts	100% <100%> (ø)	⬆️

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[graywolf336]

I like it overall. I understand this is just for slash commands, but is the thread id now being sent as part of the regular messages? Aka will the MessageSent events which are fired include the thread id?

[d-gubert]

Yes, now they include the threadId.

I've opted to not send the actual thread message object as this would add another trip to the db, and then if some app needs the data from the thread message they can call MessageReader.getById()

[graywolf336]

Wonder if we should add documentation to the property about that, that way people don't have to searching through issues and pull requests to get that information.

[graywolf336]

Suggested change

	* if any.
	* if any. Use the message reader to get the thread's message.

[d-gubert]

Updated it (see below). WDYT? 😛