Record Accessor in out_http's uri

A useful feature for the out_http module would be the capability to use tags and parts of the message to build the URI.

For example, using these two messages:

```json
{
"time": 1663711983,
"program": "foo",
"user": "bob",
"type": "app1"
},
{
"time": 1663711983,
"program": "bar",
"user": "alice",
"type": "app2"
}
```
If we want to output these to an HTTP server, we could use the out_http module. If we want to send different "types" to different endpoints on the same server, we could leverage those fields to route them using the accessor:

```ini
[OUTPUT]
name http
match *
host example.com
uri /log/$type
```

At the moment, this would require use of multiple outputs matching different tags. Being able to dynamically build the URL using the tags themselves as well as parts of the message would allow much greater flexibility for out_http users.