See https://github.com/silverstripe/silverstripe-framework/issues/9232.
Also simplifies composer instructions a bit:
- Removes composer update --no-dev references, that's a bit of an edge case that people can just discover on getcomposer.org if they need it
- Changed example from the unused and oudated silverstripe/forum to silverstripe/blog
- Updated example versions to 4.x
- Remove "updating composer" section, it now tells you if its out of date
- Remove ss-auto-git-ignore module reference. The module hasn't been updated in ages, and it's much less necessary now that all relevant modules are on composer
- Add .env example config to getting started docs, I didn't realise it was stripped from the default --prefer-dist composer install
* Remove installer
* Remove exposed install files
* Replace Dev/Install classes still in use
* Update changelog
* FIX make the grid field actions consistent to what they look like on pages
Resolves https://github.com/silverstripe/silverstripe-admin/issues/904
* Docs changes
