fix(external docs): Fix sink compression options

[wbew]

Closes #6975

This PR adds proper handling for sink compression options beyond none and gzip. As a user noted in discord, the kafka sink compression section is currently incorrect.

Sample output for the Kafka sink.

"compression": {
                        "common": true,
                        "description": "The compression strategy used to compress the encoded event data before transmission.\n\nSome cloud storage API clients and browsers will handle decompression transparently,\nso files may not always appear to be compressed depending how they are accessed.",
                        "name": "compression",
                        "required": false,
                        "warnings": [],
                        "type": {
                            "string": {
                                "default": "none",
                                "enum": {
                                    "none": "No compression.",
                                    "gzip": "[Gzip](https://www.gzip.org/) standard DEFLATE compression.",
                                    "lz4": "[lz4](https://lz4.github.io/lz4/) compression.",
                                    "snappy": "[Snappy](https://google.github.io/snappy/) compression.",
                                    "zstd": "[zstd](https://zstd.net) compression."
                                },
                                "syntax": "literal"
                            }
                        }
                    },

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[jszwedko]

Awesome, thanks for this fix!