Place large text files under annex

primarily triggered by having large `.dandi/assets.json` which forbid pushing to github!

I think we should

1. adjust our gitattributes to limit text files only to small (under 10m) with smth like

```
sed -i -e 's,\(largefiles=\)\(((mimeencoding=binary)and(largerthan=0))\) *$,\1(\2or(largerthan=1m)),g' .gitattributes
```

2. although datalad seems to add that setting on its calls (which added to my confusion to grasp what is going on), we better set it repository wide, to `git annex config --set annex.dotfiles true` . See more reasoning etc in https://git-annex.branchable.com/bugs/add__58___inconsistently_treats_files_in_dotdirs_as_dotfiles/#comment-7cc61b369ef41313313ee3fcfc2581bc

Start with .gitattributes and the large .dandi/assets.json case described in the issue, then inspect how repository-wide git-annex configuration is handled. Verify the proposed text-file size rule and annex.dotfiles setting against a representative large dot-directory file; done means such files are placed under annex and can be pushed without the reported GitHub failure.

Written by the indexing model from the issue text.