[Feature] Disconnect Toolbox from echarts.connect

### What problem does this feature solve?

Right now I have connected a few of my charts using ```echarts.connect``` [(docs)](https://echarts.apache.org/en/api.html#echarts.connect)

However, it also connects the toolbox from all the charts, so when using the ```magicType``` or ```saveAsImage``` feature, it will do these actions on all the connected charts. This will generate images of all the plots, instead of only the plot in question.

```
toolbox: {
show: true,
orient: 'vertical',
left: 'right',
top: 'center',
feature: {
mark: { show: true },
dataView: { show: true, readOnly: false },
magicType: { show: true, type: ['line', 'bar', 'stack'] },
restore: { show: true },
saveAsImage: { show: true }
}
},
```

The dataView does only display the data for the correct plot.

### What does the proposed API look like?

An solution would be to have an extra parameter in toolbox like this:

```
toolbox: {
show: true,
orient: 'vertical',
left: 'right',
top: 'center',
feature: {
mark: { show: true },
dataView: { show: true, readOnly: false },
magicType: { show: true, type: ['line', 'bar', 'stack'] },
restore: { show: true },
saveAsImage: { show: true }
},
connect: false
},
```

Where connect would default to ```false```

Start by tracing how echarts.connect propagates toolbox actions, then compare that behavior with the existing dataView handling. Evaluate the proposed toolbox connect option and verify that magicType and saveAsImage can remain local while chart connections continue to coordinate charts. Done means the behavior and default are covered by the relevant tests.

Written by the indexing model from the issue text.