Add default value for SearchBar component

[tonai]

It would be great to have the ability to set a default value for the SearchBar component without having to redeclare the whole input using the renderInput props.

I will propose a PR to add an additional defaultValue props.

[tonai]

I proposed a PR but in fact I am wondering, why not proposing an inputProps props like the Input component ?

[tonai]

We could also maybe do the same for the button, for example it is not possible now to disable the Searchbar (or maybe you prefer a disabled attribute ?).

[enguerranws]

@tonai I agree, we could have an inputProps:InputProps and a submitButtonProps:ButtonProps props. Are you working on this?

[tonai]

@enguerranws in fact I created a PR to manage the defaultValue part and afterwards I realized that we could go further and wanted to start the discussion about inputProps.
The first PR has been merged, so we now have defaultValue, but we could still propose a new one for inputProps and submitButtonProps.
For now I didn't start anything because I wasn't sure it was the right thing to do.