[GeoMechanicsApplication] Add undrained behavior support

[indigocoral]

Description

Kratos currently lacks a clear way to run undrained geotechnical analyses (i.e., no drainage/near-incompressible response with excess pore pressure generation). Add an “undrained” option that enables stable undrained response in relevant geo/poromechanics workflows.

Acceptance criteria

• Allow users to activate undrained conditions via MaterialParameters.json ["IGNORE_UNDRAINED": false] (would this still be the way to do it?)

• Unit/integration tests added and documented

Steps to take

1. Write documentation on the sequence of implementation of the formulations
2. Finding the steering mechanism that replaces the "IGNORE_UNDRAINED"
3. Implement

Documents

• https://files.seequent.com/PLAXIS/Manuals/PLAXIS_2D/English/PLAXIS_2D_3_Material%20Models%20Manual.pdf (Page 19)

[aronnoordam]

from my personal point of view, i find IGNORE_UNDRAINED a confusing parameter name. I find IS_UNDRAINED or IS_DRAINED more logical.

Or something like DRAINAGE_TYPE, but i leave it up to you, i don't have very strong oppinions about it