Sometimes it's preferred to load components & data only when activating a tab, instead of loading

all tabs (and associated data) when rendering the `<b-tabs>` set.

Individual `<b-tab>` components can be lazy loaded via the `lazy` prop, which when set doesn't mount

the content of the `<b-tab>` until it is activated (shown), and will be un-mounted when the tab is

deactivated (hidden):

<b-tabs>

<b-tab title="abc">

<!-- this content will always be mounted -->

<div>Tab ABC content</div>

</b-tab>

<b-tab title="xyz" lazy>

<!-- this content will not be mounted until this tab is shown -->

<!-- and will be un-mounted when hidden -->

<my-xyz-component></my-xyz-component>

</b-tab>

</b-tabs>

One can also make all tab's lazy by setting the `lazy` prop on the parent `<b-tabs>` component:

<b-tabs lazy>

<b-tab title="abc">

<!-- this content will not be mounted until this tab is shown -->

<!-- and will be un-mounted when hidden -->

<div>Tab ABC content</div>

</b-tab>

<b-tab title="xyz">

<!-- this content will not be mounted until this tab is shown -->

<!-- and will be un-mounted when hidden -->

<my-xyz-component></my-xyz-component>

</b-tab>

</b-tabs>