[Sophos]: Support for current Sophos XG Syslog (Version 21.5)

### Integration Name

Sophos [sophos]

### Dataset Name

sophos.xg

### Integration Version

5.15.0

### Agent Version

9.0.0

### OS Version and Architecture

Ubuntu 24.04

### User Goal

Good Afternoon!

1) The first two links in the integration description are outdated. (explaining the utm and xg dataset).

2) Also, there does not seem to be a "Default" option on the Sophos GUI anymore, so the integration package text needs to be adjusted.

Additionally, the pipeline sometimes fails to correctly parse a good amount of packets.

3) For the WAF, the fields "src_ip" and "dst_ip" are used by the WAF, but the pipeline expects "localip" and thus the parsed documents end up being less useful (having the ips under sophos.src_ip and thus not triggering anything built on ECS).

4) The pipeline processor requires the "dst_mac", which is not present on some logs sent by Sophos, leading to partly parsed packets. (tested on version 5.13.0 of the integration)
I recommend setting the switch to ignore the processor when the field is unavailable.

I ll update this issue if I find more problems.

### Existing Features

The currently supported sophos log version is from 2018 and outdated, producing the errors mentioned above.

### What did you see?

Incompletely parsed packets, packets with pipeline errors.

### Anything else?

The most up to date doku for the sophos syslog format seems to be [21.5](https://docs.sophos.com/nsg/sophos-firewall/21.5/pdf/sf-syslog-guide-21.5.pdf) .

What kind of information could I provide that helps you most?
- Anonymized syslog input that produces errors in my deployment could be an option (in very small amounts).
- I could also try to debug on my own deployment and document all the changes I made to my own pipelines until they work sufficiently correct for me.
- Please tell me if you will be adjusting the integration based on the 21.5 doku anyways, then I would just wait.

I ll also link to this tracking Issue as it is related: [#13766](https://github.com/elastic/integrations/issues/4077)