add config for body parser size

[bestwnh]

PR for https://github.com/Requarks/wiki/issues/2797 This need to restart node to make it work. The hint should include this. But I don't know how to combine with the locale files. So I just leave it with key and you can add the locale files to control the display text.

I don't familiar with the structure of this project. I just learn by some exist codes. But I do test the result and it work fine for me.

[AlexisTonneau]

Great PR ! I forgot to change the hardcoded value after an update and wasn't able to change my pages with schemas...

[testn]

Can we get this in?