Adds Cycle Motif Support

[shenoynikhil]

Support for cycle motif. Based on #6255

• Adds cycle motif class
• Adds test for cycle motif
• Updated CHANGELOG

Doubt [Remove if cleared]

I have not added node classification labels (I guess these motifs don't have them)

[codecov]

Codecov Report

Merging #6256 (0d0ac96) into master (f622fee) will decrease coverage by 1.86%.
The diff coverage is n/a.

❗ Current head 0d0ac96 differs from pull request most recent head f490606. Consider uploading reports for the commit f490606 to get more accurate results

@@            Coverage Diff             @@
##           master    #6256      +/-   ##
==========================================
- Coverage   86.42%   84.55%   -1.87%     
==========================================
  Files         377      377              
  Lines       20974    20937      -37     
==========================================
- Hits        18126    17704     -422     
- Misses       2848     3233     +385     

Impacted Files	Coverage Δ
torch_geometric/nn/models/dimenet_utils.py	0.00% <0.00%> (-75.52%)	⬇️
torch_geometric/nn/models/dimenet.py	14.90% <0.00%> (-52.76%)	⬇️
torch_geometric/profile/profile.py	33.33% <0.00%> (-25.39%)	⬇️
torch_geometric/nn/conv/utils/typing.py	83.75% <0.00%> (-15.00%)	⬇️
torch_geometric/nn/pool/asap.py	92.10% <0.00%> (-7.90%)	⬇️
torch_geometric/nn/inits.py	67.85% <0.00%> (-7.15%)	⬇️
torch_geometric/resolver.py	82.75% <0.00%> (-6.90%)	⬇️
torch_geometric/nn/dense/linear.py	85.40% <0.00%> (-5.91%)	⬇️
torch_geometric/transforms/add_self_loops.py	94.44% <0.00%> (-5.56%)	⬇️
torch_geometric/nn/models/attentive_fp.py	95.83% <0.00%> (-4.17%)	⬇️
... and 29 more

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[wsad1]

Looks good mostly. Left some comments.