Move loading of custom HTML headers and static assets

[poettig]

This change is necessary for greenpau/caddy-security#290, further explanation over there.

It loads custom HTML headers and static assets at the same time that custom js path and custom css path get loaded instead of arbitrarily loading them when reading the Caddyfile in caddy-security.

[greenpau]

@poettig , this looks good! Thank you!

Please add CLA
https://github.com/greenpau/go-authcrunch/blob/main/CONTRIBUTING.md#contributor-license-agreements

[github-actions]

CLA Assistant Lite bot All contributors have signed the CLA ✍️ ✅

[greenpau]

@poettig , please see here how to agree to CLA. https://github.com/contributor-assistant/github-action#demo-for-step-2-and-3

[poettig]

I have read the CLA Document and I hereby sign the CLA

[poettig]

@greenpau Sorry, I overlooked the CONTRIBUTING.md and then had to clean up / rebase with upstream on this branch first. It should be all cleared up now :)

[greenpau]

@poettig , please follow https://github.com/greenpau/go-authcrunch/blob/main/CONTRIBUTING.md#contributor-license-agreements. 2 requirements. Apologies for the confusion.

Once it is done, I will merge and release go-authcrunch and update caddy-security accordingly.

[poettig]

@greenpau No worries, I should have read CONTRIBUTING.md again after rebasing. I followed the steps and added my consent to the yml.

[greenpau]

@poettig , thank you for contributing 👍