Adds Bellman ford algorithm and its test cases.

[Kpraful]

This PR adds BellmanFord algorithm and its test cases following the guideline and references from previous code.

• I have performed a self-review of my code
• My code follows the style guidelines of this project
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Comments in areas I changed are up to date
• I have added comments to hard-to-understand areas of my code
• I have made corresponding changes to the README.md

[siriak]

Could you decompose the algorithm into smaller functions so that it's easier to read and maintain?

[codecov]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (fe4b357) 96.04% compared to head (3ad6dde) 96.03%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #416      +/-   ##
==========================================
- Coverage   96.04%   96.03%   -0.02%     
==========================================
  Files         230      231       +1     
  Lines        9592     9665      +73     
==========================================
+ Hits         9213     9282      +69     
- Misses        379      383       +4     

Files	Coverage Δ
Algorithms/Graph/BellmanFord.cs	94.52% <94.52%> (ø)

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[Kpraful]

Could you decompose the algorithm into smaller functions so that it's easier to read and maintain?

Hi, I have made changes in code, Please have a look, And thank you for swift resolution of issues.

[Kpraful]

Hi, Can you please review PR.

[Kpraful]

Followed the requested review and break it into smaller functions

[Kpraful]

Reviewed changes

[Kpraful]

Made changes as adviced.

[siriak]

Looks good, thanks!