Export isAlertSelectorAvailable

[MarcBuch]

In addition to isDashboardSelectorAvailable, it would be great to export isAlertSelectorAvailable as well.

Why?

This allows the usage of EntitySwitch on the EntityPage. Instead of throwing an error, if there are not Grafana annotations, the card then is simply not rendered.

EntitySwitch Example

<EntitySwitch>
  <EntitySwitch.Case if={isDashboardSelectorAvailable}>
    <Grid item xs={3}>
      <EntityGrafanaDashboardsCard />
    </Grid>
  </EntitySwitch.Case>
</EntitySwitch>
<EntitySwitch>
  <EntitySwitch.Case if={isAlertSelectorAvailable}>
    <Grid item xs={3}>
      <EntityGrafanaDashboardsCard />
    </Grid>
  </EntitySwitch.Case>
</EntitySwitch>

[K-Phoen]

Thanks! :)