[doc/man3][OSSL_ENCODER] Move NOTES to the bottom
For consistency with `OSSL_DECODER.pod`, and `man-pages(7)`, the `NOTES`
section is moved at the end of the file.
According to `man-pages(7)` the recommended section order is:
> NAME
> SYNOPSIS
> CONFIGURATION [Normally only in Section 4]
> DESCRIPTION
> OPTIONS [Normally only in Sections 1, 8]
> EXIT STATUS [Normally only in Sections 1, 8]
> RETURN VALUE [Normally only in Sections 2, 3]
> ERRORS [Typically only in Sections 2, 3]
> ENVIRONMENT
> FILES
> VERSIONS [Normally only in Sections 2, 3]
> CONFORMING TO
> NOTES
> BUGS
> EXAMPLE
> SEE ALSO
This commit does not attempt to fix the order in all pages but focuses
only on `OSSL_ENCODER` which has a "twin" man page in `OSSL_DECODER`,
making the inconsistent section order quite jarring.
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/13932)