build: support prefixed version tags in docker-release workflow

[davidaparicio]

Description

This PR enhances the docker-release workflow to support both prefixed and unprefixed version tags. The workflow now accepts tags in two formats:

• Standard semantic version: 1.2.3
• Prefixed version: cloudflare-exporter-1.2.3

When a prefixed tag is used, the prefix is automatically stripped before building the Docker image, ensuring the image is tagged with the clean version number.

Type of Change

• New feature (non-breaking change which adds functionality)

Testing

• I have run make pr-tests and all tests pass
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Code Quality

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation

Additional Notes

Changes made:

• Updated .github/workflows/docker-release.yaml to accept tags matching pattern cloudflare-exporter-[0-9]+.[0-9]+.[0-9]+
• Added version extraction step that strips the cloudflare-exporter- prefix if present
• Applied the extracted version to both the build-and-push and copy-to-dockerhub jobs
• Backward compatible: existing unprefixed tags (e.g., 1.2.3) continue to work as before

Motivation:

This change provides flexibility in tagging releases, allowing for more descriptive tag names while maintaining clean version numbers in Docker image tags.

[davidaparicio]

Related with the issue #178 😉