[DOCS] Document database records

[linawolf]

A detailed explanation of what they are was missing.

This is a preparation for documenting the
v13 additions of record objects.

Releases: main, 12.4

[github-actions]

The backport to 12.4 failed:

The process '/usr/bin/git' failed with exit code 1

stderr

error: could not apply 27c7a83fb... [DOCS] Document database records
hint: After resolving the conflicts, mark them with
hint: "git add/rm <pathspec>", then run
hint: "git cherry-pick --continue".
hint: You can instead skip this commit with "git cherry-pick --skip".
hint: To abort and get back to the state before "git cherry-pick",
hint: run "git cherry-pick --abort".
hint: Disable this message with "git config advice.mergeConflict false"

stdout

Auto-merging Documentation/ApiOverview/ContentElements/Index.rst
Auto-merging Documentation/ApiOverview/Database/Index.rst
CONFLICT (content): Merge conflict in Documentation/ApiOverview/Database/Index.rst
Auto-merging Documentation/ExtensionArchitecture/Extbase/Reference/Domain/Model.rst

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-12.4 12.4
# Navigate to the new working tree
cd .worktrees/backport-12.4
# Create a new branch
git switch --create backport-4760-to-12.4
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick 27c7a83fba3519a0f2d81376149271bc7b199058,269ebdf67ee632c8d8216ec61069f6cef7f3dc39,c7776e34098802fd641e3acc58d53cadd936f63d,3166049e003b88714dcbda9efb71a9ff8c6550db,00a77b5fe7a4f89f1e0b1beaf2f6f312b4f0f682,afab71095eb96ac0853f8dfffce14509d8a77d86,e1586a47bb60e007712de1b6e4490aba95a798fc,87c034ce9f2a16a4d9216e13cad95bf19179486d,dfaf460fa9a993cd6dd2189fdefe966c122901f9,b9d260a372c0f87d9a1336affa69d0ba67911e6b
# Push it to GitHub
git push --set-upstream origin backport-4760-to-12.4
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-12.4

Then, create a pull request where the base branch is 12.4 and the compare/head branch is backport-4760-to-12.4.