[gdb] Move ChangeLog files to archive dir

We stopped updating ChangeLog files in 2021, and they are no longer
maintained.

If I want to see history, I use git log, so I don't use them for any purpose.

And they're in my way when I'm searching for files, grepping, or refactoring
using sed.

Move them out of the way, into a root-level directory named archive
(alternative names: legacy, deprecated, attic, stale, historical,
unmaintained).

Result of:
...
for f in $(find gdb* -name "ChangeLog*"); do
    dir=$(dirname $f)
    f=$(basename $f)
    u=archive/$dir
    mkdir -p $u
    git mv $dir/$f $u/$f
done
...

Also drop ignoring ChangeLog files in some pre-commit tools.

A less impactful but also less effective change would be to move <dir>/ChangeLog
into <dir>/archive/ChangeLog.