Add fish completion support

[sikmir]

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[LinuxSuRen]

There are some errors that need to be fixed. I will do it due to it is not caused by this PR. And thanks for your time.

[LinuxSuRen]

I removed some outdated config and tests. #773

hi @sikmir , please update your branch from the master branch. Thanks.

[sikmir]

I removed some outdated config and tests. #773

hi @sikmir , please update your branch from the master branch. Thanks.

Updated, but still failing.