Introduce env vars for prefix and suffix body content surrounding Changelog

[tajobe]

Adds BODY_PREFIX and BODY_SUFFIX optional environment variable configurations to enable augmenting release body contents around the Changlog entries.

For example, I want a suffix after my Changlog in each release explaining the various artifacts produced in the release (fat jar vs online download)

---

An alternative implementation might be a single variable for eg BODY_FORMAT, which could used something like fmt.Sprintf(rel.BodyFormat, rel.Changelog)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.14%. Comparing base (ec9c5b5) to head (18abcd2).
Report is 16 commits behind head on main.

Additional details and impacted files

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##             main     #145   +/-   ##
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  Coverage   95.14%   95.14%           
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  Files           2        2           
  Lines         309      309           
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  Hits          294      294           
  Misses         10       10           
  Partials        5        5           

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[Copilot]

Pull Request Overview

This PR introduces two new environment variables, BODY_PREFIX and BODY_SUFFIX, to allow custom content to be added before and after the changelog in the release body. Key changes include:

• Replacing the Changelog field with a Body field across the release, modal, and test files.
• Adding new configuration fields and a GetBody method in config.go.
• Updating documentation and CHANGELOG.md to reflect the new environment variables.

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
release/release_test.go	Updated test cases to use Body instead of Changelog.
release/release.go	Changed release payload to reference Body rather than Changelog.
release/modal.go	Renamed the Changelog field to Body in the Release struct.
main.go	Updated main function to assemble the release body using GetBody.
config.go	Added new configuration fields (BodyPrefix, BodySuffix) and GetBody.
README.md	Documented the new BODY_PREFIX and BODY_SUFFIX environment variables.
CHANGELOG.md	Noted the addition of BODY_PREFIX and BODY_SUFFIX for release bodies.

[anton-yurchenko]

Thanks @tajobe, that is a good idea.
I will evaluate the full template approach aside (#146)