feat(command line): add a configurable completion timer delay

[dyl10s]

This resolves #1105

[theol0403]

Thanks for the PR! Can you modify the settings flow to match the rest of the extension, like https://github.com/vscode-neovim/vscode-neovim/blob/master/src/extension.ts#L20?

[dyl10s]

Thanks for the PR! Can you modify the settings flow to match the rest of the extension, like https://github.com/vscode-neovim/vscode-neovim/blob/master/src/extension.ts#L20?

Refactored it, let me know if there are any other standards that I am not following here that you would like me to adjust!