Support template format

It would be helpful to support the template format. I would particularly like to be able to see the vulnerability location and CVE in the output. Locally I can achieve this with the following template:

```
"Package","Version Installed","Vulnerability ID","Severity","Locations"
{{- range .Matches}}
"{{.Artifact.Name}}","{{.Artifact.Version}}","{{.Vulnerability.ID}}","{{.Vulnerability.Severity}}","{{ (index .Artifact.Locations 0).RealPath }}"
{{- end}}
```

which, with `grype -o template -t ./csv.tmpl [IMAGE NAME]`, I can get an output like:

```csv
"Package","Version Installed","Vulnerability ID","Severity","Locations"
"apt","2.6.1","CVE-2011-3374","Negligible","/usr/share/doc/apt/copyright"
"binutils","2.40-2","CVE-2023-1972","Negligible","/usr/share/doc/binutils/copyright"
```

I'd be willing to create a PR if you are interested.

Start by tracing how the action handles scan output options and whether it passes a template format and template path through to Grype, using the issue's `grype -o template -t ./csv.tmpl` example as the behavioral reference. Done means the action can accept and apply a template so vulnerability locations and CVE identifiers appear in its output, with validation added where the existing project structure requires it.

Written by the indexing model from the issue text.