Cache the results of go-template execution

### TL;DR

In render_action.go, we use the Go `text/template` library to "execute" a string that may contain template expression like `Hello, {{.person}}`. In some cases we might execute the same template repeatedly, and we might be able to save time by caching the results instead executing the same template string again.

We should wait to do this until we have some evidence that our existing approach isn't fast enough.

### Detailed design

_No response_

### Alternatives considered

_No response_

### Additional information

_No response_