Get rid of deadlock in the query to address_current_token_balance table

[vbaranov]

Motivation

Deadlock detected:

blocked_pid | blocked_user | blocking_pid | blocking_user |
19697 | poa          |         2809 | poa           | SELECT t0."name", t0."symbol", t0."total_supply", t0."decimals", t0."type", t0."cataloged", t0."holder_count", t0."contract_address_hash", t0."inserted_at", t0."updated_at" FROM "tokens" AS t0 WHERE (t0."contract_address_hash" = ANY($1)) ORDER BY t0."contract_address_hash" FOR UPDATE
2809 | poa          |        19697 | poa           | SELECT t0."name", t0."symbol", t0."total_supply", t0."decimals", t0."type", t0."cataloged", t0."holder_count", t0."contract_address_hash", t0."inserted_at", t0."updated_at" FROM "tokens" AS t0 WHERE (t0."contract_address_hash" = ANY($1)) ORDER BY t0."contract_address_hash" FOR UPDATE

This PR should speed up the import of blocks

Changelog

Add a distinct clause in a selection of contract_address_hash from address_current_token_balance table

Otherwise, duplicated contract_address_hashes cause deadlocks in the next series of queries:
SELECT t0.* FROM "tokens" AS t0 WHERE (t0."contract_address_hash" = ANY($1)) ORDER BY t0."contract_address_hash" FOR UPDATE

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

[coveralls]

Pull Request Test Coverage Report for Build abe1ae93-3428-4e87-9735-9130dccef547

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.01%) to 75.229%

---

Files with Coverage Reduction	New Missed Lines	%
apps/block_scout_web/lib/block_scout_web/controllers/chain/market_history_chart_controller.ex	2	71.43%

Totals
Change from base Build 903a5cce-cc23-4282-8868-a2a7df32f12a:	-0.01%
Covered Lines:	5333
Relevant Lines:	7089

---

💛 - Coveralls