Extend token symbol type varchar(255) -> text

[vbaranov]

Motivation

2022-09-26T12:03:33.059 [error] Task #PID<0.1157.39> started from Indexer.Fetcher.Token terminating
** (Postgrex.Error) ERROR 22001 (string_data_right_truncation) value too long for type character varying(255)
    (ecto_sql 3.7.1) lib/ecto/adapters/sql.ex:760: Ecto.Adapters.SQL.raise_sql_call_error/1
    (ecto 3.7.1) lib/ecto/repo/schema.ex:744: Ecto.Repo.Schema.apply/4
    (ecto 3.7.1) lib/ecto/repo/schema.ex:367: anonymous fn/15 in Ecto.Repo.Schema.do_insert/4
    (explorer 4.1.8) lib/explorer/chain.ex:4853: anonymous fn/5 in Explorer.Chain.update_token/2
    (ecto 3.7.1) lib/ecto/multi.ex:716: Ecto.Multi.apply_operation/5
    (elixir 1.13.1) lib/enum.ex:2396: Enum."-reduce/3-lists^foldl/2-0-"/3
    (ecto 3.7.1) lib/ecto/multi.ex:690: anonymous fn/5 in Ecto.Multi.apply_operations/5
    (ecto_sql 3.7.1) lib/ecto/adapters/sql.ex:1021: anonymous fn/3 in Ecto.Adapters.SQL.checkout_or_transaction/4
Function: &Indexer.BufferedTask.log_run/1
    Args: [%{batch: [%Explorer.Chain.Hash{byte_count: 20, bytes: <<175, 187, 17, 28, 237, 44, 90, 176, 124, 112, 62, 65, 232, 68, 22, 128, 16, 77, 160, 162>>}], ...

Changelog

Extend token symbol type varchar(255) -> text

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