Implement addconnection key in graph files to specify post-deployment connections with specific types

[pinheadmz]

Closes #814

Includes cleanups:

• bump bitcoin core default version to 31.0
• cleans up dag_connection scenario so the dag_connection test can cover the new graph values

example, added to test/data/ten_semi_unconnected

nodes:
  - name: tank-0000
  - name: tank-0001
  - name: tank-0002
  - name: tank-0003
    addconnection:
      - to: tank-0004
        type: block-relay-only
  - name: tank-0004
    addconnection:
      - to: tank-0006
        type: addr-fetch
  - name: tank-0005
    addconnection:
      - to: tank-0006
      - to: tank-0007
        v2: false
  - name: tank-0006
  - name: tank-0007
  - name: tank-0008
    addnode:
      - tank-0009
  - name: tank-0009