Adds examples for Log4j 2's JSON format log template layout

[joon-shin-ddhq]

What does this PR do? What is the motivation?

The Java Log Collection docs are missing an example of a JSON layout template for the Log4j 2 appender. This template is necessary for Java apps to emit logs in JSON format, but the docs don't provide one. As someone who doesn't work with Java regularly, it took me quite a while to track down a working example. Judging from this Slack thread, I wasn’t the only one who ran into this.

https://dd.slack.com/archives/C4W013KEU/p1749835158457139

I have added the following to this doc page:

• Adds a full example for Log4j 2's JSON format log template layout file, MyLayout.json
• Adds an instruction to remove dd.trace_id and dd_span.id from the template layout examples, if the log and trace correlation is not used.

Please have a Java Log Collection PM or an APM Injection Platform PM review these changes.

Merge instructions

Merge readiness:

• [] Ready for merge

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Additional notes