website: fix RSS feed for security page

[vladlen]

Summary

Increase RSS feed items for Security Advisory and
Errata Notice from 10 to 20.
Fix publication date format to RFC 822 according to
RSS 2.0 requirements (across all language versions of
the page /security, /ru/security, /zh-tw/security )

Fixes https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=295989

[ziaee]

1. 20 is too short. Can we have 50?
2. why does this combine security and errata if we have two separate feeds for that?
3. can we please put the actual content in these?

[ziaee]

nevermind on 50, seems like we do not want that.

[carlavilla]

Coz if you put in two, you will break the current """"API""""", people will complain

[vladlen]

In D57725#1323489, @ziaee wrote:

1. 20 is too short. Can we have 50?
2. why does this combine security and errata if we have two separate feeds for that?
3. can we please put the actual content in these?

I can make additional RSS-feed for SA and EN pages (they both have default RSS feed with 0 items),
it could be additional task, but our colleagues ask to fix this interface.
Could we proceed with it?

[carlavilla]

In D57725#1330090, @vladlen wrote:

In D57725#1323489, @ziaee wrote:

1. 20 is too short. Can we have 50?
2. why does this combine security and errata if we have two separate feeds for that?
3. can we please put the actual content in these?

I can make additional RSS-feed for SA and EN pages (they both have default RSS feed with 0 items),
it could be additional task, but our colleagues ask to fix this interface.
Could we proceed with it?

if you split it in two (in a different task), please, *please*, first send an email to announce@