[Feature] Guide does not cover gradle toolchain

[sreich]

Hello, the openliberty docs generally cover usage of it with gradle, but in this case, there are only maven samples available.

Can this be corrected?

[gkwan-ibm]

We aware of this for long time, but we still have no good design to show both gradle and maven instruction.

[gkwan-ibm]

a dup of OpenLiberty/guides-common#46