libcurl: Restrict redirect schemes (follow-up)

- Allow FTPS on redirect.

- Update default allowed redirect protocols in documentation.

Follow-up to 6080ea0.

Ref: https://github.com/curl/curl/pull/4094

Closes https://github.com/curl/curl/pull/4115

lib/url.c

@@ -488,7 +488,8 @@ CURLcode Curl_init_userdefined(struct Curl_easy *data)
      define since we internally only use the lower 16 bits for the passed
      in bitmask to not conflict with the private bits */
   set->allowed_protocols = CURLPROTO_ALL;
-  set->redir_protocols = CURLPROTO_HTTP | CURLPROTO_HTTPS | CURLPROTO_FTP;
+  set->redir_protocols = CURLPROTO_HTTP | CURLPROTO_HTTPS | CURLPROTO_FTP |
+                         CURLPROTO_FTPS;
 
 #if defined(HAVE_GSSAPI) || defined(USE_WINDOWS_SSPI)
   /*