Issue with HTTP2 shading

[Goksi]

Describe the bug
While shading javalin ssl inside of spigot plugin, hpack http2 class is not included inside of ServiceLoaders, resulting
ERR_CONNECTION_CLOSED
Fixed by adding org.apache.maven.plugins.shade.resource.ServicesResourceTransformer transformer. Docs should be updated accordingly.

Screenshots

[zugazagoitia]

@tipsy assign me and I'll work on it over the weekend (can't assign myself)

[zugazagoitia]

The docker tutorial #177 should also be reviewed.

javalin/javalin#1840 is relevant here.

[tipsy]

Done, thanks !

[tipsy]

Pretty long weekend @zugazagoitia !