feat(CLI): Use positional arguments in envd destroy and so on

[gaocegege]

Description

Now the destroy command does not look great:

envd destroy --name {name}

Expected:

envd destroy {name}

We should wait until urfave/cli#1074 is resolved.

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[gaocegege]

Maybe, we should migrate to https://github.com/spf13/cobra

It supports this feature.

[kemingy]

Maybe, we should migrate to https://github.com/spf13/cobra

It supports this feature.

LGTM. A huge refactor.

[kemingy]

urfave/cli may have better shell-completion (both bash and zsh) support.