Ignore git submodule from commits

[vga91]

Ignore git submodule via git update-index --assume-unchanged apoc-core,
in build.core and init script, so that after building the project or executing an ./gradlew --init-script init.gradle <cmd> will be hidden from a later git add ..

Note that if I directly git add . before either of these 2 steps above,
the sumbodule will appear in the staging area

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Alternative:
Document somewhere (maybe here) that e.g. git add . also adds the submodule,
so we possibly need to remove it with git restore --staged apoc-core.

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Other attempts:
ignore=all or ignore = dirty in .gitmodules hide the submodule with git status but not with git add ..

.gitignore seeems not to work properly