Mattermost-server: Add bool type argument to the slash command autocomplete

[iomodo]

Right now supported argument types for autocomplete are Text, StaticList and DynamicList. Add AutocompleteArgTypeBool as another type.
User should be able to:

1. Create a command with boolean arguments(use AddBoolArgument, AddNamedBoolArgument method names).
2. Input positional bool arguments as t, f, true or false
3. Input named bool arguments as --name. If --name is present we assume argument value is true, if not argument value is false.

User input parsing is done here

Changes should be done only on a server.

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JIRA: https://mattermost.atlassian.net/browse/MM-25530

[KrishnaSindhur]

hi, i am interested to solve this issue