Overhaul allocation documentation (technical reference)

[SouthEndMusic]

During/after the current allocation developments, significant portions of the allocation documentation has to be rewritten. There are:

The allocation concept docs (docs/concept/allocation.qmd) which is aimed at modelers. A quick run trough yields:

• [x] the section Vertical fluxes and local storage needs to be updated with the new Basin concept
• [x] a section on linearized physical relationships needs to be added (maybe to The optimization constraints)
• [x] the storage and level variables have to be added to The optimization variables
• [x] Separate flow and level objections have to be added to The optimization objective

The allocation developer docs (docs/dev/allocation.qmd). These are probably very outdated, so these either have to be removed or updated if we think that is worth the effort.

@jarsarasty

[ghost]

Lex to write documentation based on the current code written by Bart and Bart to review