chore: ci updates

[bonddim]

This pull request includes several updates to the repository's CI/CD configuration, dependency management, and documentation. The most important changes are the usage of GoReleaser for release workflow, the introduction of Dependabot for automated dependency updates and the removal of Travis CI config file and links.

CI/CD Improvements:

• Added Dependabot configuration to automate dependency updates for GitHub Actions workflows. (.github/dependabot.yaml)
• Consolidated multiple release workflows into a single goreleaser job, updating the GitHub Actions versions used and simplifying the configuration. (.github/workflows/binaries.yml)
• Updated the Go testing workflow to use the latest versions of GitHub Actions

Configuration Additions:

• Added a new GoReleaser configuration file to streamline the release process for binaries and docker images. (.goreleaser.yaml)

Documentation Updates:

• Updated the README to replace Travis CI badges with GitHub Actions badges and added a badge for Go version.

Cleanup:

• Removed the obsolete Travis CI configuration file. (.travis.yml)

Closes #58
Closes #59
Closes #63

Resolves #35
Resolves #64

[bonddim]

@a8m ,
Here you may see the updated:
workflow - https://github.com/bonddim/envsubst/actions/runs/13672120589/job/38224467325
artifacts - https://github.com/bonddim/envsubst/releases/tag/v1.4.4
images - https://github.com/bonddim/envsubst/pkgs/container/envsubst

PS: This PR is ready to merge with Rebase and Merge strategy to preserve commit history.