fix(VOtpInput): update the otp when value changes

[TheoPez]

Description

Update the otp input when value changes.
fixes #14437

Motivation and Context

This pull request solves the update problem present on the new VOtpInput component. Indeed, it is impossible to change or to empty the field, even during the reset of a form (see the reproduction in #14437 )

How Has This Been Tested?

Markup:

<template>
  <v-container>
    <v-form ref="form">
      <v-otp-input
        v-model="otp"
      ></v-otp-input>
    </v-form>
    <v-btn @click="$refs.form.reset()">Reset Button</v-btn>
    <v-btn @click="otp = '123'">change otp value to : 123</v-btn>
    {{otp}}

  </v-container>
</template>

<script>
  export default {
    data: () => ({
      otp: '0'
    }),
  }
</script>

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Improvement/refactoring (non-breaking change that doesn't add any features but makes things better)

Checklist:

• The PR title is no longer than 64 characters.
• The PR is submitted to the correct branch (master for bug fixes and documentation updates, dev for new features and backwards compatible changes and next for non-backwards compatible changes).
• My code follows the code style of this project.
• I've added relevant changes to the documentation (applies to new features and breaking changes in core library)

[johnleider]

Please create unit tests that correlate to the changes made in this request.