pub fn insert_entry(self, value: MetadataValue<VE>) -> OccupiedEntry<'a, Ascii> {
        OccupiedEntry {
            inner: self.inner.insert_entry(value.inner),
            phantom: PhantomData,
        }
    }
Insert the value into the entry.

The value will be associated with this entry's key. The new
`OccupiedEntry` is returned, allowing for further manipulation.

# Examples

```
# use tonic::metadata::*;
let mut map = MetadataMap::new();

if let Entry::Vacant(v) = map.entry("x-hello").unwrap() {
let mut e = v.insert_entry("world".parse().unwrap());
e.insert("world2".parse().unwrap());
}

assert_eq!(map.get("x-hello").unwrap(), "world2");
```
tonic/src/metadata/map.rs