mantle-demo - Yup custom validation for mnemonic

[TdfGomes]

I saw in a commit that doing a 12 words validation was commented as a TODO. In AuBit I did like this:

const validationSchema = Yup.object().shape({
    mnemonic: Yup.string()
      .test('mnemonic', function(value) {
        let errorMessage
        if (value)) {
          if (value.split(' ').length !== 12) {
            errorMessage = 'Mnemonic should have 12 words'
          }
        } else {
          errorMessage = 'This field is required'
        }
        return this.createError({ path: this.path, message: errorMessage })
      })
  })

Just an idea! you might want to go from here.

[makevoid]

very nice, I think we should pick up this

[ayrbox]

regex can also be used. Please consider following mnemonic validation in e2e testing for generated mnemonic

https://github.com/appliedblockchain/base-app/pull/48/files#diff-5fd0af204b6a3027f0e61a448976fc89R16

const wordCount = mnemonic.match(/(\w+)\s{0,1}/g).length
expect(wordCount).toEqual(12)