Admin: Set up button in Anti-Spam card doesn't activate Akismet

#### Steps to reproduce the issue

1. Install, activate, and connect Jetpack.
2. Purchase a Security bundle.
3. Navigate to `wp-admin -> Plugins` and deactivate Akismet.
4. Navigate to `wp-admin -> Jetpack dashboard -> At a Glance`.
5. Click the `Set up` button in the `Anti-spam` card.
6. The UI isn’t very useful:
* If you click `Continue`, you end up on your My Plan page in Calypso.
* If you wait a few seconds, the banner disappears, and the text `Nothing to do here…` appears.
7. Navigate back to `wp-admin -> Plugins` and notice that Akismet wasn’t activated.
8. Navigate back to `wp-admin -> Jetpack dashboard -> At a Glance` and notice that the `Set up` button still appears in the `Anti-Spam` card.

The same behavior occurs if Akismet is not installed. The `Set up` button does not install Akismet.

#### What I expected
I think the intention is that clicking the `Set up` button should install/activate Akismet.

Reproduce the flow from the Jetpack dashboard’s At a Glance page with Akismet deactivated or not installed, then inspect the Anti-spam card’s Set up entry point. Done means the action installs Akismet when needed, activates it when inactive, and no longer leaves the Set up button or misleading UI state behind.

Written by the indexing model from the issue text.