Separate FIRST_BLOCK and TRACE_FIRST_BLOCK option for blocks import and tracing methods

[vbaranov]

Motivation

Currently, we have FIRST_BLOCK and LAST_BLOCK to manage the range of blocks to index. But, for instance, the archive node can be partially archive node: there is no archive state until a specific block number. In that setup, Blockscout will not import any block less than FIRST_BLOCK, if it is set up. The idea is to add more flexibility and to separate block import and tracing methods to be available to import blocks from partial archive node even without internal transactions.

Changelog

TRACE_FIRST_BLOCK and TRACE_LAST_BLOCK are added

Checklist for your Pull Request (PR)

• I added an entry to CHANGELOG.md with this PR
• If I added new functionality, I added tests covering it.
• If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.
• I checked whether I should update the docs and did so by submitting a PR to https://github.com/blockscout/docs
• If I added/changed/removed ENV var, I submitted a PR to https://github.com/blockscout/docs to update the list of env vars at https://github.com/blockscout/docs/blob/master/for-developers/information-and-settings/env-variables.md and I updated the version to master in the Version column. Changes will be reflected in this table: https://docs.blockscout.com/for-developers/information-and-settings/env-variables.
• If I add new indices into DB, I checked, that they are not redundant with PGHero or other tools