No Config is generated for a plugin with only a Goto Definition Request Handler

In #4126, I noticed the CI was green, even though the PR doesn't modify the vscode extension schema json file.

The reason seems to be in https://github.com/haskell/haskell-language-server/blob/master/hls-plugin-api/src/Ide/Plugin/ConfigUtils.hs#L114, we only generate an "Enable Plugin" config, if there is exactly one other config. However, we don't generate a config for `Goto Definition` handlers.

I think, we should also generate an "Enable Plugin" Config, if no other config exists.