[Doc] Document security model

[pitrou]

Describe the enhancement requested

Following internal conversations, it was suggested that we document Arrow's security model. There are guidelines here:
https://cwiki.apache.org/confluence/display/SECURITY/Documenting+your+security+model

This issue can probably decompose into several sub-issues:

• security model for the Arrow specs (in-memory format, IPC, etc.)
• security model for the Arrow C++ components and APIs (such as the IPC, Parquet, CSV readers)
• ...

Component(s)

C++, Documentation, Format

[pitrou]

cc @wgtmac @zanmato1984 @adamreeve @alamb @tustvold @WillAyd

[alamb]

We document a similar thing for arrow-rs here: https://github.com/apache/arrow-rs/tree/main/arrow#safety