Duplicate links in contributing.md

### Relevent telegraf.conf

```toml
N/A
```


### System info

N/A

### Docker

_No response_

### Steps to reproduce

N/A

### Expected behavior

N/A

### Actual behavior

N/A

### Additional info

The links for Resources at the end of the CONTRIBUTING page has duplicate links (Logging, Packaging). We should de-duplicate them.