Add repr to ComponentGraph and use in PipelineBase

[angela97lin]

Closes #2204 by adding repr to the ComponentGraph class and then cleaning up PipelineBase's repr to reuse ComponentGraph's repr.

On main:

After this PR:

[codecov]

Codecov Report

Merging #2565 (41082fd) into main (3b5bf62) will increase coverage by 0.1%.
The diff coverage is 100.0%.

@@           Coverage Diff           @@
##            main   #2565     +/-   ##
=======================================
+ Coverage   99.9%   99.9%   +0.1%     
=======================================
  Files        285     285             
  Lines      26103   26115     +12     
=======================================
+ Hits       26069   26081     +12     
  Misses        34      34             

Impacted Files	Coverage Δ
evalml/pipelines/component_graph.py	100.0% <100.0%> (ø)
evalml/pipelines/pipeline_base.py	99.7% <100.0%> (-<0.1%)	⬇️
...valml/tests/pipeline_tests/test_component_graph.py	100.0% <100.0%> (ø)

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[chukarsten]

Awesome sauce. I always get sad when the built ins aren't defined.