Document memory management for Kestra

[tchiotludo]

Following all the discoveries in #https://github.com/kestra-io/cloud-instances/issues/75, we need to add some documentation that explains the behavior publicaly.

@gperreymond will draft the documentation and @aj-emerich will help.

[gperreymond]

kestra-jvm-active-processor-blog.md

@aj-emerich @tchiotludo
Here my proposal

[aj-emerich]

What's the intent here: blog post, documentation, or both?

[gperreymond]

Dunno what ludo wants on this one ; But I wrote like a post blog because i can't found a good way to write a documentation.

[aj-emerich]

I can handle that. There's enough here for me to transform it into that content type.

[tchiotludo]

@aj-emerich maybe asked @loicmathieu some details about the underlying reason (why having too many core could increase the memory usage), it's not self-explanatory