Fix `--allow-missing-relations-in-first-blocks`

[khorolets]

Currently, account_changes constraints cast this feature to a useless one.

Plan to adjust the non-strict mode to:

• [ ] turn off account_changes handler in the non-strict mode for the number of blocks provided
• [ ] decrease the number of retries to be performed in non-strict mode (currently every retry increases the delay between tries)

This should allow us to start indexer from any block to speed up catching up or something similar in emergency situations.

[khorolets]

While working on this I've realized it's pointless and there is no way to fix it.

We don't be able to switch between non-strict and strict modes smoothly. In case of missing data, we've skipped in a non-strict mode at any point after switching to a strict mode can lead us to the situation where would try to store account_changes record and affecting an Account that was created during the non-strict mode. We miss the corresponding Receipt, we aren't able to save account_change related to that account.

We decided to drop --allow-missing-relations-in-first-blocks in favor to create --non-strict-mode which just makes the node to work in that mode unless stopped.