feat(utils): Create relative_utils module for topic relationship management

[ashelly]

Topic: create_relative_utils
relative: commit_with_topic

Extract utility functions for modifying Relative: tags in commit messages.

[ashelly]

Reviews in this chain:
└#18 Feature: common utils for end-to-end tests
　├#10 Feature: Tree command to Show Stack
　│├#19 Feature: Tests for tree (stack show) command
　│└#9 feat(edit): Add revup edit command with safety features
　│　└#12 test(edit): Add tests for edit safety features
　│　　└#21 Docs: Describe new features
　└#3 Feature: Revup commit gains --topic and --relative to pre-populate commit message
　　└#13 feat(utils): Create relative_utils module for topic relationship management
　　　├#14 Feature: amend --relative fixes stack
　　　│├#17 Tests(amend): Tests for amend behavior, especially --relative
　　　│└#4 Feature: Revup commit gains --draft flag
　　　│　└#20 Feature: tests for the --draft flag
　　　└#15 feat(restack): Add --as argument for bulk topic reordering
　　　　└#16 test(restack): Add tests for --as argument and GCA algorithm

[ashelly]

#	head	base	diff	date	summary
0	48cf9278	62542d50	diff	Feb 3 18:15 PM	3 files changed, 619 insertions(+), 54 deletions(-)
1	3171aa70	4662dff2	diff	Feb 3 18:23 PM	1 file changed, 3 insertions(+), 3 deletions(-)
2	bac27783	45af35ce	diff	Feb 4 17:37 PM	0 files changed