[Doc][C++] Document supported Parquet encryption features

[asfimport]

In ARROW-10918 we started documenting the Parquet format features supported by parquet-cpp, but I left a TODO for encryption features.

Reporter: Antoine Pitrou / @pitrou
Assignee: Gidon Gershinsky / @ggershinsky

Related issues:

• [C++][Doc] Document supported Parquet features (relates to)

PRs and other links:

• GitHub Pull Request #8974

_{Note: This issue was originally created as ARROW-10941. Please see the migration documentation for further details.}

[asfimport]

Antoine Pitrou / @pitrou:
@thamht4190 @ggershinsky

[asfimport]

Gidon Gershinsky / @ggershinsky:
On it

[asfimport]

Antoine Pitrou / @pitrou:
Issue resolved by pull request 8974
#8974