Feat: Support on-premise github enterprise

[suaaaaa]

What does this PR introduce?

Currently, only github.com API is supported, so it has been added to support github enterprise.

• add GITHUB_API_URL and pass it as baseURL

Related issues

• closes #162

Reviewers

• @benschwarz for engineering review
• @thefoxis for content and copy review

[CLAassistant]

All committers have signed the CLA.

[benschwarz]

@suaaaaa looks good to me, could you provide an example of how enterprise users can configure it? I’d like to ensure the readme includes the new functionality.

(Feel free to post the technical info, I can help with writing the documentation phrasing 😎)

[suaaaaa]

@suaaaaa looks good to me, could you provide an example of how enterprise users can configure it? I’d like to ensure the readme includes the new functionality.

(Feel free to post the technical info, I can help with writing the documentation phrasing 😎)

@benschwarz Thank you😃 GITHUB_API_URL is passed as the baseURL, so Enterprise users do not need to configure anything. What if the README image action offers added support for github enterprise?

Image Actions offers:

• Fast, efficient and near-lossless compression
• Best image compression algorithms available (mozjpeg and libvips)
• Ease of customisation: use default settings or adapt to your needs
• Running on demand or schedule
• Support GitHub Enterprise

[benschwarz]

@suaaaaa Sounds good, could you add the bullet point as "Supports GitHub Enterprise" to README.md?

[suaaaaa]

@benschwarz Added and committed👍

[thefoxis]

if there's no need to configure anything for GitHub Enterprise customers, then the changes look good to me 😄 thank you, @suaaaaa!