SSVC Deployer Decision Points doc is out of date

[ahouseholder]

Describe the bug

At some point in the recent past, we changed the Deployer decision model to use Automatable instead of Utility (which was comprised of Automatable and Value Density). While this change happened in our code, we did not update the accompanying markdown documentation.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://certcc.github.io/SSVC/howto/deployer_tree/#deployer-decision-points
2. Observe that we list "Utility" instead of "Automatable"

Expected behavior

Update https://github.com/CERTCC/SSVC/blob/main/docs/howto/deployer_tree.md to reflect the Utility → Automatable change.

[ahouseholder]

Linking for posterity:

• Replace Utility with Automatable in Deployer Tree #238 was the issue that original prompted the change
• Replace Utility with Automatable in Deployer tree #248 was the PR that made the change