Not able to drop many empty blocks onto landing page at once and fill the blocks config one after one.

Steps to reproduce:

1. Go to landing page creator,
2. Create a new landing page,
3. Drop many blocks on a landing page,
4. Try to edit one of them using config popup,
5. Submit form data to render block preview,
6. The validation disallow getting preview when all the blocks required config is not provided.

Expected result:
The preview should be updated. It should be possible to drop many blocks and provide the config later, for each block separately.

Suggested solution:
We should have a flag telling us that the drop has just been dropped onto the landing page workspace and the config has not been provided yet.
It should prevent from landing page validation.
The flag should change its state when opening a config popup for the first time. Then the config should be required with no excuse.