Revamp FD/triage sections

<Beuc> I've been meaning to propose this change (dropping no-dsa) for a while but never did, so I'm in favor of this change :)
<Beuc> I'd volunteer to tighten the Development page on FD as it became quite verbose over time, too.
<el_cubano> Beuc: Could you put together a change and tag me on the MR?
<Beuc> let's do that
<santiago> ACTION: stop using <no-dsa> for (E)LTS in favor or the more precise <postponed> and <ignored> tags. Beuc to update the Development page

• discontinue use of "no-dsa" as discussed in 2024-03-25 IRC meeting
• regroup triage information in:
  • security tracker presentation: for all contributors
  • tagging: for all contributors
  • initial triage: for FD, reworked as:
    • guiding principles and tooling
    • reference criteria to consider and weigh (converting previous ad-hoc incomplete list of cases)
  • package addition tooling
  • maintainers contact procedures and templates
• add section "Handling related packages"
• merge duplicate information
• drop some obsolete information
• use concise writing and bullet points over lenghty paragraphs, for faster initial read and efficient later reference

Tagging @roberto as promised :)