TLS docs fixes for <programlisting>

While working with TLS I noticed that the password callback definition had an
extra newline in the programlisting in the docs. Since the <programlisting>
has been indented with the textblock, the newline comes from whitespace being
significant. The attached 0001 fixes by instead anchoring <programlisting> on
column zero like how most of the docs do it. Grepping around I found one more
instance of the same pattern which is also included.

The "Enter PEM pass phrase" prompt was referred to in one place with <literal>
and one with <programlisting>, the 0002 settles on using <literal> for both
since IMO that makes the docs more readable. While there, it also fixes the
spelling of "pass phrase" from the two variations we had (of which none was the
correct one from src/backend/libpq/be-secure-openssl.c as well as the OpenSSL
file crypto/pem/pem_lib.c).

cheers ./daniel