Fixes after review

After discussion, we decided to simplify attribute translation for now. Full translation requires support for UTF-8 values encoded according to RFC 8187/7230, this can be clarified and implemented in further PRs.

1. Remove translation tables
2. Use simple translation rules only, for now ignoring UTF-8 keys and values

- `X-Attribute-NEOFS-` prefixed headers considered well-known system attributes
- System Attribute key is uppercased
- System Attribute key's `-` translates to `_`
- `X-Attribute-` prefixed headers considered regular object attributes
- Normal attribute key is a result of http header prefix trimming
- Value string should be left as is, for now

```
HTTP:
X-Attribute-NEOFS-Expiration-Epoch: 123
X-Attribute-FileName: cat.jpg

NeoFS:
__NEOFS__EXPIRATION_EPOCH: "123"
FileName: "cat.jpg"
```

Signed-off-by: Evgeniy Kulikov <kim@nspcc.ru>

upload.go

@@ -103,7 +103,7 @@ func (a *app) upload(c *fasthttp.RequestCtx) {
 		}
 	}
 
-	filtered := a.hdr.Filter(&c.Request.Header)
+	filtered := filterHeaders(a.log, &c.Request.Header)
 	attributes := make([]*object.Attribute, 0, len(filtered))
 
 	// prepares attributes from filtered headers