feat: add channels to event lineage graph

[Cali0707]

Fixes #7682

Proposed Changes

• Add channel to event lineage graph as a vertex
• Add another vertex and edge to the graph if there is a DLS for the channel
• Unit tests for both scenarios

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Cali0707

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[Cali0707]

/cc @Leo6Leo @creydr @pierDipi

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.15%. Comparing base (c9de4b5) to head (a31d490).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7745      +/-   ##
==========================================
+ Coverage   69.11%   69.15%   +0.04%     
==========================================
  Files         339      339              
  Lines       19398    19429      +31     
==========================================
+ Hits        13406    13437      +31     
  Misses       5330     5330              
  Partials      662      662              

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[Leo6Leo]

/lgtm

[Cali0707]

/retest-required