Add home page for Stakeholder Decision ~~Models~~ Tables

[ahouseholder]

Is your feature request related to a problem? Please describe.
There is no single landing page for the concept of Decision Table. We have a number of pages for individual decision models:

• https://certcc.github.io/SSVC/howto/supplier_tree/
• https://certcc.github.io/SSVC/howto/deployer_tree/
• https://certcc.github.io/SSVC/howto/coordination_intro/
• https://certcc.github.io/SSVC/howto/cvss_v4/

but there is no top-level page for the section currently titled "Stakeholder Decision Models"

Relevant excerpt from mkdocs.yml:

    - Stakeholder Decision Models:
        - Supplier Decision Model: 'howto/supplier_tree.md'
        - Deployer Decision Model: 'howto/deployer_tree.md'
        - Coordinator Decision Models:
          - About Coordination: 'howto/coordination_intro.md'
          - Coordination Triage: 'howto/coordination_triage_decision.md'
          - Publication Decision: 'howto/publication_decision.md'
        - CVSS v4 Analyst Models:
            - About CVSS v4: 'howto/cvss_v4/index.md'
            - Equivalence Set 1: 'howto/cvss_v4/eq1.md'
            - Equivalence Set 2: 'howto/cvss_v4/eq2.md'
            - Equivalence Set 3: 'howto/cvss_v4/eq3.md'
            - Equivalence Set 4: 'howto/cvss_v4/eq4.md'
            - Equivalence Set 5: 'howto/cvss_v4/eq5.md'
            - Equivalence Set 6: 'howto/cvss_v4/eq6.md'
            - Qualitative Severity: 'howto/cvss_v4/qualitative.md'

Describe the solution you'd like

1. Add a page to serve as the home page for Stakeholder Decision Tables
2. Rename the navigation to refer to Decision Table instead of Decision Model in the links to each individual page.
3. Update the content of each page in this section to use Decision Table consistently instead of Decision Model.

Additional context

Related to #1100 and follow-up tasks.