[Documentation] update FAQ

[lixuna]

Describe the update: update FAQ

Describe why update is needed

• CNF WG (and CNCF’s related Cloud Native Telco efforts) has moved to LFN (see wiki)
• what we have now: https://github.com/lfn-cnti/certification/blob/main/faq.md

Tasks

• [x] Draft new FAQ based on new CNTI Certification process
• [x] Cost: replace CNCF mentions and links with LF Networking mentions and links. No fee for members, The fee is the same as joining LF Networking.
• [ ] Participation form url blocked by #69
• [x] CNF Certification - replace wording to reflect CNTI Certification (reference: https://wiki.lfnetworking.org/display/LN/Certification)
• [ ] Score: blocked by #82
• [x] Questions: Replace email address to lfn-cnti@lfnetworking.org