Add Support for Array and Key-Value Attributes

Hi,

Currently, there seems to be no way to add array or key-value attributes using the `--attrs` argument.
For example, the attribute `container.image.tags` has a type of `string[]` ([documentation](https://opentelemetry.io/docs/specs/semconv/attributes-registry/container/)).

It would be helpful to enable creating spans with array attributes such as `otel-cli span --attrs "container.image.tags=[aaa,bbb]"`

Alternatively, introducing a new argument such as `--attrs-json` to allow specifying attributes in JSON would also be a viable.

Start by locating the --attrs argument parsing and the tests covering scalar attributes. Compare the requested array syntax with the alternative JSON form before choosing a supported input shape. Done means spans created through the CLI accept array and key-value attributes, with tests covering the new parsing behavior.

Written by the indexing model from the issue text.