Set infinite timeout for fetch_min_missing_block_cache method DB query

[vbaranov]

Motivation

{"error":{"initial_call":null,"reason":"** (DBConnection.ConnectionError) tcp recv: closed (the connection was closed by the pool, possibly due to a timeout or because the pool has been terminated)\n    (ecto_sql 3.5.3) lib/ecto/adapters/sql.ex:751: Ecto.Adapters.SQL.raise_sql_call_error/1\n    (ecto_sql 3.5.3) lib/ecto/adapters/sql.ex:684: Ecto.Adapters.SQL.execute/5\n    (ecto 3.5.5) lib/ecto/repo/queryable.ex:229: Ecto.Repo.Queryable.execute/4\n    (ecto 3.5.5) lib/ecto/repo/queryable.ex:17: Ecto.Repo.Queryable.all/3\n    (ecto 3.5.5) lib/ecto/repo/queryable.ex:149: Ecto.Repo.Queryable.one/3\n    (explorer 0.0.1) lib/explorer/chain.ex:2687: Explorer.Chain.fetch_min_missing_block_cache/0\n    (explorer 0.0.1) lib/explorer/chain/cache/min_missing_block.ex:28: Explorer.Chain.Cache.MinMissingBlockNumber.fetch_min_missing_block/0\n    (elixir 1.11.4) lib/task/supervised.ex:90: Task.Supervised.invoke_mfa/2\n"},"logging.googleapis.com/sourceLocation":{"file":null,"line":0,"function":null},"message":"Task #PID<0.18593.19> started from Explorer.Chain.Cache.MinMissingBlockNumber terminating\n** (DBConnection.ConnectionError) tcp recv: closed (the connection was closed by the pool, possibly due to a timeout or because the pool has been terminated)\n    (ecto_sql 3.5.3) lib/ecto/adapters/sql.ex:751: Ecto.Adapters.SQL.raise_sql_call_error/1\n    (ecto_sql 3.5.3) lib/ecto/adapters/sql.ex:684: Ecto.Adapters.SQL.execute/5\n    (ecto 3.5.5) lib/ecto/repo/queryable.ex:229: Ecto.Repo.Queryable.execute/4\n    (ecto 3.5.5) lib/ecto/repo/queryable.ex:17: Ecto.Repo.Queryable.all/3\n    (ecto 3.5.5) lib/ecto/repo/queryable.ex:149: Ecto.Repo.Queryable.one/3\n    (explorer 0.0.1) lib/explorer/chain.ex:2687: Explorer.Chain.fetch_min_missing_block_cache/0\n    (explorer 0.0.1) lib/explorer/chain/cache/min_missing_block.ex:28: Explorer.Chain.Cache.MinMissingBlockNumber.fetch_min_missing_block/0\n    (elixir 1.11.4) lib/task/supervised.ex:90: Task.Supervised.invoke_mfa/2\nFunction: #Function<0.83273533/0 in Explorer.Chain.Cache.MinMissingBlockNumber.\"-fun.fetch_min_missing_block/0-\">\n    Args: []","severity":"ERROR","time":"2021-06-23T14:16:37.208Z"}

when query execution takes more than 6o seconds (default timeout)

Changelog

Set infinity timeout fetch_min_missing_block_cache method DB query

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