[Website]: Document increasing the NoFile Ulimit to not hit too many open files when using TBS

[lucabelluccini]

Type of issue

None

What documentation page is affected

https://www.elastic.co/docs/solutions/observability/apm/apm-server/tail-based-sampling

What happened?

We should document how to increase the nofile ulimit on most supported OSes when enabling Tail Based Sampling (TBS).

Additional info

No response