Fix typos and update workflow, docs, and aliases

[zhongwencool]

Corrected the spelling of 'changlog.md' to 'CHANGELOG.md' and updated references in docs.exs. Fixed a typo in the homepage_url in docs.exs. Modified the GitHub Actions workflow to trigger on both push and pull_request events. Added 'ex_doc' to the 'check' alias in rebar.config.

[Copilot]

Pull request overview

This PR fixes typos and improves the project's documentation and CI configuration. The changes correct file references and URLs, enhance the GitHub Actions workflow to trigger on pull requests, and add documentation generation to the build check.

• Corrected file path and URL typos in docs.exs
• Updated GitHub Actions workflow to trigger on both push and pull_request events
• Added ex_doc to the rebar.config check alias for documentation validation

Reviewed changes

Copilot reviewed 2 out of 4 changed files in this pull request and generated no comments.

File	Description
rebar.config	Added ex_doc to the check alias to include documentation generation in quality checks
docs/CHANGELOG.md	New changelog file with project history (corrected filename from changlog.md)
docs.exs	Fixed typos in file path (changlog.md → CHANGELOG.md) and homepage URL (obsever_cli → observer_cli)
.github/workflows/erlang.yml	Updated trigger configuration to run on both push and pull_request events

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