Bug 20292: Filter/censor info sent via SIP

Bug 20292: Filter/censor info sent via SIP

Some libraries would like to limit the amount of personal information a SIP server sends
to arbitrary parties on a per-login basis.

Test Plan:
1) Add a new key/value pair to one of your existing login stanzas in your SIP config file
   For example: hide_fields="BD,BE,BF,PB"
2) Restart SIP
3) Send a SIP message that would normally return those fields ( in this example, a Patron Information Request )
4) Note the response has had those fields removed

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Christopher Davis <tubaclarinet@protonmail.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>