Documenting snapshot builds

[LikeTheSalad]

Explaining users how to use snapshot versions in their projects

[Copilot]

Pull request overview

This PR adds user-facing documentation for consuming snapshot (main-branch) builds of the OpenTelemetry Android artifacts, and adjusts release automation to keep README version references up to date.

Merge Tier: 3 (build/release automation changes)

Changes:

• Document how to add Sonatype’s snapshot repository and depend on *-SNAPSHOT BOM versions in Gradle.
• Update the release-branch preparation workflow’s README version rewrite to avoid matching the new snapshot example.
• Extend the version update script to also bump the README’s snapshot BOM version when versions are advanced.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
README.md	Adds a new “Snapshot Builds” section with Gradle configuration and BOM usage example.
.github/workflows/prepare-release-branch.yml	Narrows the README BOM version rewrite pattern so it won’t affect -SNAPSHOT lines.
.github/scripts/update-version.sh	Updates the README snapshot BOM version alongside gradle.properties version bumps.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65.67%. Comparing base (3bc3ab2) to head (d14aff8).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1977   +/-   ##
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  Coverage   65.67%   65.67%           
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  Files         172      172           
  Lines        3918     3918           
  Branches      442      442           
=======================================
  Hits         2573     2573           
  Misses       1213     1213           
  Partials      132      132           

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[fractalwrench]

LGTM