Please describe what the rule should do:
Similar to the core ESLint ruleno-negated-condition (and its autofixable variantunicorn/no-negated-condition), this rule would report negated conditions in the template (only if bothif andelse cases are handled). Avoiding unnecessary negated conditions makes the code a bit easier to read.

What category should the rule belong to?
[ ] Enforces code style (layout)
[ ] Warns about a potential error (problem)
[x] Suggests an alternate way of doing something (suggestion)
[ ] Other (please specify:)

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

<template>  <div><!-- BAD-->    <divv-if="!foo" />    <spanv-else /><!-- GOOD-->    <spanv-if="foo" />    <divv-else />  </div></template>

Additional context
Should it also report ternaries with negated conditions used in the template?

<template>  <div><!-- BAD-->    <div:class="!foo ? 'bar' : 'baz'" /><!-- GOOD-->    <div:class="foo ? 'baz' : 'bar'" />  </div></template>

Or should that be a different rule? Then the names could bevue/no-negated-condition for theno-negated-condition extension rule that applies to ternaries, andvue/no-negated-v-if-condition for the rule proposed above.