fix(GlToggle): Show help text from slot

What does this MR do?

Allows users of <gl-toggle> to pass the help text in a slot without defining it as a prop.

Before

I can only show the help if I pass a help prop.

<gl-toggle
  v-model="on"
  help="!! A VALUE IS NEED HERE !!"
>
  <template #help>
    Help message!
  </template>
</gl-toggle>

After

I can directly use the slot.

<gl-toggle
  v-model="on"
>
  <template #help>
    Help message!
  </template>
</gl-toggle>

Verifying locally

Changing the story locally helped me confirm this fix:

1. Apply the diff below
2. Run yarn storybook
3. Visit http://localhost:9001/?path=/docs/base-toggle--default

diff to add slot

diff --git a/src/components/base/toggle/toggle.stories.js b/src/components/base/toggle/toggle.stories.js
index a5e8435b..57679332 100644
--- a/src/components/base/toggle/toggle.stories.js
+++ b/src/components/base/toggle/toggle.stories.js
@@ -31,12 +31,13 @@ const Template = (args, { argTypes }) => ({
     <gl-toggle
       v-model="value"
       :disabled="disabled"
-      :help="help"
       :label-id="labelId"
       :is-loading="isLoading"
       :label="label"
       :label-position="labelPosition"
-    />
+    >
+      <template #help>Help slot works!</template>
+    </gl-toggle>
   </div>`,
 });

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines.
• GitLab UI's contributing guidlines.
• If it changes a Pajamas-compliant component's look & feel, the MR has been reviewed by a UX designer.
• If it changes GitLab UI's documentation guidelines, the MR has been reviewed by a Technical Writer.
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  • GitLab: mr_url
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  • Status Page: mr_url
• Added the ~"component:*" label(s) if applicable.

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• Security reports checked/validated by a reviewer from the AppSec team

Accessibility

If this MR adds or modifies a component, take a few moments to review the following:

• All actions and functionality can be done with a keyboard.
• Links, buttons, and controls have a visible focus state.
• All content is presented in text or with a text equivalent. For example, alt text for SVG, or aria-label for icons that have meaning or perform actions.
• Changes in a component’s state are announced by a screen reader. For example, changing aria-expanded="false" to aria-expanded="true" when an accordion is expanded.
• Color combinations have sufficient contrast.