Add autocomplete suggestions

[iomodo]

Summary

This PR will add slash command autocomplete suggestions.

[codecov-commenter]

Codecov Report

Merging #40 into master will decrease coverage by 2.60%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master      #40      +/-   ##
==========================================
- Coverage   21.03%   18.42%   -2.61%     
==========================================
  Files           6        6              
  Lines         233      266      +33     
==========================================
  Hits           49       49              
- Misses        173      206      +33     
  Partials       11       11              

Impacted Files	Coverage Δ
server/command.go	0.00% <0.00%> (ø)
server/main.go	0.00% <ø> (ø)
server/plugin.go	36.84% <ø> (ø)

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[jfrerich]

@iomodo, this is awesome and I can't wait to add it to other plugins! I have a one change request (up for discussion)

[jfrerich]

Suggested change

	queue.AddTextArgument("Creates a post for user with the given message for the next meeting date.", "message", "")
	queue.AddTextArgument("Message for the next meeting date.", "message", "")

[jfrerich]

The text here is describing the meaning of the Message autocomplete option. I think it makes sense to somehow tell the user Message is not an autocomplete value, but an input needed from the user.

On the same point, I wonder if we could/should somehow designate the difference between an autocomplete value versus an input required from the user. As an example, next-week is an autocomplete value and Message requires free text from the user.

[iomodo]

Agree. What we could do is differentiate using icons on the left side, or have different styles, but it is not yet part of the Server PR. I'll create the ticket for this.
I'd suggest using [message] for now.

[jfrerich]

That'd be perfect. Thanks!

[hanzei]

Is this a backwards compatibly change? Does min_server_version need to get bumped?

[iomodo]

@hanzei There will be no changes for older servers, new functionality will not work of course. No min_server_version bump is needed. We need a dependency bump to 5.24 though, to be able to compile the new autocomplete data.

[jfrerich]

Thanks @iomodo! I'm stealing this as a reference for other plugins :)

[levb]

why this version?

[iomodo]

This was the latest master, we will switch it to 5.24

[hanzei]

v5.24-rc1 is out: https://github.com/mattermost/mattermost-server/releases/tag/v5.24.0-rc1

[DHaussermann]

I have tested all the auto-complete functionality

• All commands work as expected (except schedule)
• All argument name and descriptions look correct except schedule (see below)
• Tested the updated plugins on server 5.23.1 to ensure it works as expected without auto complete

@iomodo one question here... The schedule command functionality has changed instead of Mon or Monday you have to use 1 Was this part of this PR or do you know anything about it? I can't see a separate PR for it. In my opinion this is less usable. Also in it's current state it's wrong as the description says it will accept 1-5 however, you can schedule meetings on Saturday and Sunday with 6 and 7

[DHaussermann]

Tested and passed

• Schedule is now working as expected
• Confirmed setting works with use of auto complete
• Regression tested that you can use partial such as fri
• Regression tested that week days are case insensitive
  LGTM!
  Thanks @iomodo fir fixing this.