Changes

contrib/jenkins: publish binaries

Publish binaries to:
https://ftp.osmocom.org/binaries/osmo-rp2040-firmware/

Put each target into a separate directors as users are typically
interested in one specific product/board:
  .
  ├── iso7816_cardem
  │   ├── all
  │   │   ├── iso7816_cardem-0.1.0-3-g2fda293.elf
  │   │   └── iso7816_cardem-0.1.0-3-g2fda293.uf2
  │   └── latest
  │       ├── iso7816_cardem.elf
  │       └── iso7816_cardem.uf2
  └── osmo-gtm900
      ├── all
      │   ├── osmo-gtm900-0.1.0-3-g2fda293.elf
      │   └── osmo-gtm900-0.1.0-3-g2fda293.uf2
      └── latest
          ├── osmo-gtm900.elf
          └── osmo-gtm900.uf2

Related: OS#6784
Change-Id: Ic22d693bfebc33278033514fa5900866454e499f