Rule Proposal: label-spacing

[MunMunMiao]

Please describe what the rule should do:
Increase readability by adding tag spacing

What category should the rule belong to?

• Enforces code style
• Warns about a potential error
• Suggests an alternate way of doing something
• Other (please specify:)

Provide 2-3 code examples that this rule should warn about:

• close{before: false, after: false}

<!-- bad -->
<template>
    <div class="header"></div>
    <div class="content"></div>
    <div class="footer"></div>
</template>

• open{before: true, after: true}

<!-- good -->
<template>
    <!-- spacing -->
    <div class="header"></div>
    <!-- spacing -->
    <div class="content"></div>
    <!-- spacing -->
    <div class="footer"></div>
    <!-- spacing -->
</template>

• only before{before: true, after: false}

<template>
    <!-- spacing -->
    <div class="header"></div>
    <!-- spacing -->
    <div class="content"></div>
    <!-- spacing -->
    <div class="footer"></div>
</template>

• only after{before: false, after: true}

<template>
    <div class="header"></div>
    <!-- spacing -->
    <div class="content"></div>
    <!-- spacing -->
    <div class="footer"></div>
    <!-- spacing -->
</template>

• more examples

<template>
    <!-- spacing -->
    <div class="header">
        <!-- spacing -->
        <div class="logo"></div>
        <!-- spacing -->
    </div>
    <!-- spacing -->
    <div class="content">
        <!-- spacing -->
        <div class="left"></div>
        <!-- spacing -->
        <div class="right"></div>
        <!-- spacing -->
    </div>
    <!-- spacing -->
    <div class="footer">
        <!-- spacing -->
        <span>XXXXX(at)gmail.com</span>
        <!-- spacing -->
    </div>
    <!-- spacing -->
</template>

Additional context

[FloEdelmann]

This should now be possible with the vue/padding-line-between-tags rule (added in #1966).