Feature Request - Loop by pattern matching.

I have a case where I need to create multiple entries in a config file based on the existence of environment variables. (its for a reverse proxy and I want to be able to add new entries simply by adding additional environment variables)

Something like:

**Env Vars:**
```
SRVCS_FIRST_HOSTNAME=sample.service.com
SRVCS_FIRST_DEST=internal.server.name
SRVCS_SECOND_HOSTNAME=second.service.com
SRVCS_SECOND_DEST=internal2.server.name
```

**Template:**
```
${SRVCS_*_<
host: ${HOSTNAME}
destination: ${DEST}

>}
```

**Result:**
```
host: sample.service.com
destination: internal.server.name

host: second.service.com
destination: internal2.server.name

```

Any thoughts on this idea? _I_ think it'd be pretty handy.

Look at the existing substitution logic in the Go codebase, likely in a main package or command. Understand how environment variables are currently parsed and replaced. The feature requires adding pattern matching to iterate over groups of variables (like SRVCS_*_HOSTNAME and SRVCS_*_DEST) and generating repeated blocks. Check if there are existing tests for expansion to see the expected behavior and add new tests for the loop feature.

Rédigé par le modèle d'indexation à partir du texte de l'issue.