resolves #787 add support for SSL

[amirabramovich]

resolved issue #787

[ggrossetie]

Looks good, left a few suggestions (style) and an open question.
Would you be able to write the documentation for this feature? I guess you can add a section in https://github.com/yuzutech/kroki/blob/main/docs/modules/setup/pages/configuration.adoc

I can tell you that the search term "ssl" and "https" are pretty popular on https://docs.kroki.io/ so it's definitely something users will be interested to read 😄

[amirabramovich]

Thanks for your suggestions, I made all the adjustments and added a documentation :)

[ggrossetie]

I made all the adjustments and added a documentation :)

Thanks!

I just noticed that we are using setKeyPath and setCertPath however I think it's easier to pass the contents of the private key and the certificate.

In my experience it makes things easier since you don't have a to mount a volume to provide the certificate and private key files. You can just pass the contents of the certificate and the private key as string using environment variables.

Taking this into account, I've made several suggestions.

[amirabramovich]

Thanks, I changed the path to the value itself. Please review and merge :)

[ggrossetie]

It looks good, thanks!

I made tiny changes in ServerSSLTest to assert that the deployment is failing when the SSL is enabled but KROKI_SSL_KEY is missing.

Apart from that, great work 👌🏻