find-doc-nits: Check env var documentation

find-doc-nits: Check env var documentation

Check the code (source files and .in files) for undocumented ENV
variable names. The variable name should be documented in openssl-env or
in a designated man page in the "ENVIRONMENT" section.

Resolves: https://github.com/openssl/openssl/issues/28050

Signed-off-by: Norbert Pocs <norbertp@openssl.org>
Reviewed-by: Neil Horman <nhorman@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
(Merged from https://github.com/openssl/openssl/pull/28025)