Add validator for plugin entrys

QeApp plugin uses the dictionary to collect the items that to be added. For example
```python
# this is the entry point of the plugin
hello_world ={
"outline": Outline,
"setting": Setting,
"workchain": workchain_and_builder,
"result": Result,
}
```
The workchain
```python
# register the workchain and builder
workchain_and_builder = {
"workchain": HelloWorldWorkChain,
"get_builder": get_builder,
}
```
It is better to add a validator if the plugin developer passes the wrong keywords and data type. Pydantic could be a solution.