Add new ssl headers:
'X-SSL-Client-Verify', 'X-SSL-Client-Has-Cert', 'X-SSL-Client-DN',
'X-SSL-Client-CN', 'X-SSL-Issuer', 'X-SSL-Client-SHA1',
'X-SSL-Client-Not-Before', 'X-SSL-Client-Not-After'
Allow users to send to the backend with multiple choices when
tls_terminated is enabled for client certificate.
Story: 2002165
Task: 20020
Change-Id: I112936ee85c9e0dcfb87b962176ba7d623989a30