Add individual ERTBOX per zone

[rnyb]

Related to #103

This resolves the ERT part of the issue
The issue can be closed with next RMS update

[Copilot]

Pull request overview

Updates the Drogon AHM ERT configuration to use zone-specific ERTBOX grids for APS field parameters, enabling different grid sizes per zone (as described in Issue #103) to reduce memory/disk/runtime when layer counts vary significantly between zones.

Changes:

• Updated APS field parameter configuration to reference separate ERTBOX EGRID files per zone (Valysar/Therys/Volon) and bind each FIELD parameter to the appropriate grid.
• Updated the main AHM ERT model include comment to reflect the new per-zone ERTBOX behavior.
• Cleaned up the RMS project readme instructions for compress/restore and dev update steps.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
rms/model/0readme.txt	Reformats/clarifies instructions for compressing/restoring the RMS project and documenting dev updates.
ert/model/drogon_ahm.ert	Updates the comment on the APS include to indicate per-zone ERTBOX usage.
ert/input/config/ahm_field_aps.ert	Introduces per-zone EGRID definitions and assigns each APS FIELD parameter to the correct zone-specific ERTBOX grid via GRID:.

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[oddvarlia]

Looks OK