Switch to faststart oracle image for testing

[blafond]

Quarkus has made the switch to improve bootstrapping. See this PR for details

<oracle.image>docker.io/gvenzl/oracle-xe:21-slim</oracle.image>

[blafond]

@DavideD Ran clean build locally multiple times with both oracle versions I get basically the same results for either one. ~2 minutes.

Are there more specific metrics or ways I could track?

[DavideD]

That's fine, I was expecting something similar because we only start the server once.

I've tried it on my machine:

gvenzl/oracle-xe:21.3.0-slim 
-- with image download:  BUILD SUCCESSFUL in 4m 14s
-- already downloaded :  BUILD SUCCESSFUL in 1m 27s

gvenzl/oracle-xe:21.3.0-faststart
-- with image download: BUILD SUCCESSFUL in 7m 41s 
-- already downloaded : BUILD SUCCESSFUL in 1m 15s 

The build was slightly faster when the image is available but downloading the new image was quite slow.
Not that this is a rigorous indication but I think we can continue to use the slim version for now.

Maybe there's a difference when running it on slower machines. We can reconsider this later.

Thanks