httpcaddyfile: Add a couple more placeholder shortcuts (#5015)

This adds:
- `{file.*}` -> `{http.request.uri.path.file.*}`
- `{file_match.*}` -> `{http.matchers.file.*}`

This is a follow-up to #4993 which introduces the new URI file placeholders, and a shortcut for using `file` matcher output.

For example, where the `try_files` directive is a shortcut for this:

```
@try_files file <files...>
rewrite @try_files {http.matchers.file.relative}
```

It could instead be:
```
@try_files file <files...>
rewrite @try_files {file_match.relative}
```

0 files changed, 0 insertions, 0 deletions