Bash script to auto-generate release notes.

[shivanshs9]

Closes #108

Checklist

• [ ] I have made a material change to the repo (functionality, testing, spelling, grammar)
• [x] I have read the [Contribution Guide] and my PR follows them.
• [x] I updated my branch with the development branch.
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have added necessary documentation about the functionality in the appropriate .md file
• [x] I have added in line documentation to the code I modified
• [x] I have tested it on my end on bash.

Short description of what this PR does:

• This PR adds a bash utility to auto-generate release notes, depending on the latest release tag and the current tag.
• Looks for configured changelog file, by default CHANGELOG.md, and looks for the matching tag names to find the notes to add.
• Use ./auto-release.sh -h to display help message.

[SendGridDX]

All committers have signed the CLA.

[codecov[bot]]

Codecov Report

Merging #112 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #112   +/-   ##
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  Coverage   91.46%   91.46%           
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  Files           6        6           
  Lines         293      293           
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  Hits          268      268           
  Misses         25       25

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[thinkingserious]

Hello @shivanshs9,

Thanks again for the PR!

We want to show our appreciation by sending you some swag. Could you please fill out this form so we can send it to you? Thanks!

Team SendGrid DX

[shivanshs9]

Yep, filled it. Thanks! It feels nice to help the developers, who made sendgrid possible for us!