Update beam_parameters for 2023 PbPb from ion data-taking in October 2023

We have prepared an "expected-2023" PbPb beamfile before (!203 (merged)), now the beam parameters are updated from this slides, listed as follows:

• filling scheme: 1240b with 398 colliding at IP8 (actually there are several filling schemes listed here)
• bunch intensity: 1.8 x 108 Pb ions
• beam energy: 6.8 TeV
• instantaneous lumi: 1.1 x 1027 cm-2 s-1, mu = 0.001 (no levelling)
• β*: 1.5 m
• half crossing angle: horizontal, -139 (internal) - 135 (external) = -274 μrad
• polarity: +/DOWN

The PVs are measured by @samarian , with Run Number 278788, in Fill 9237

• PVX = 1.143 mm
• PVY = 0.649 mm
• PVZ = 5.535 mm
• \sigma_{PVX} = 0.0274 mm
• \sigma_{PVY} = 0.0278 mm
• \sigma_{PVZ} = 46.89 mm

cc @gcorti @kreps @samarian