Plugin API: open_terminal() panes have 'wrong' title and run as command panes

[msirringhaus]

Issue description

When calling open_terminal() from a plugin, the newly created terminal behaves differently than one created via e.g. Alt+n

1. The title of the pane is not e.g. Pane #2, but /bin/bash (or whatever is the default shell)
2. PaneInfo has terminal_command set to Some("/bin/bash") instead of None, marking it as a command pane

    /// If this is a command pane, this will show the stringified version of the command and its
    /// arguments
    pub terminal_command: Option<String>,

Minimal reproduction

use zellij_tile::prelude::*;

use std::collections::BTreeMap;

#[derive(Default)]
struct State {}

register_plugin!(State);

impl ZellijPlugin for State {
    fn load(&mut self, _configuration: BTreeMap<String, String>) {
        request_permission(&[
            PermissionType::OpenTerminalsOrPlugins,
            PermissionType::ReadApplicationState,
        ]);
    }
    fn update(&mut self, _event: Event) -> bool {
        open_terminal("./");
        close_self();
        false
    }
    fn render(&mut self, _rows: usize, _cols: usize) {}
}

Run: zellij plugin --skip-plugin-cache -- file:/path/to/rust-plugin-example/target/wasm32-wasi/debug/rust-plugin-example.wasm
This should (after granting permissions) simply open a new pane with the described behavior.

Other relevant information

This was likely introduced with this PR: #3296