docs: rust: quick-start: update Ubuntu instructions

docs: rust: quick-start: update Ubuntu instructions

Split installation instructions for Ubuntu into 2 different sections:
- For Ubuntu 25.04: this release provides easy-to-install Rust packages.
- For Ubuntu 24.10 and below: these releases provide rust-1.80 and
  bindgen-0.65, which do not set their tools as defaults. The instructions
  for these versions have been updated to configure Rust tools properly.

Signed-off-by: Igor Korotin <igor.korotin@yahoo.com>
Link: https://lore.kernel.org/r/20250402160047.1827500-1-igor.korotin@yahoo.com
[ Dropped 24.10 -- it is soon out of support and their `bindgen` issue
  (reported as issue #2086639) was never patched anyway. Removed trailing
  spaces. Split into subheaders. Added `rustfmt` link. Removed spurious
  backquotes. Reworded contents slightly. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>