Fix flag param handling in gevulot-cli

[tuommaki]

No description provided.

[koxu1996]

This PR should not go unnoticed, as it introduced important workaround for passing single value args.

My case study

I wanted to pass foo -- bar args, so I used the following tasks' cmd_args when calling gevulot-cli exec

[{ "name": "foo", "value": "" }, { "name": "", "value": "--" }, { "name": "bar", "value": "" }]

Here is the request that was sent with CLI - request-1.json:

     ...
              "args": ["foo", "", "", "--", "bar", ""],
     ...

I was not expecting those empty strings 😿.

The solution was to update the CLI tool with cargo install --git https://github.com/gevulotnetwork/gevulot.git gevulot-cli (from #bbe20d41 to #700d759a).

Request after update - request-2.json:

     ...
              "args": ["foo", "--", "bar"],
     ...

Now everything works as expected!