Bridged tokens price feed improvement

[vbaranov]

Motivation

Improve bridged tokens price feed

Changelog

Get the price of bridged tokens from a foreign token contract address, not from symbol

Chore:

• CUSTOM_CONTRACT_ADDRESSES_TEST_TOKEN environment variable to manage test tokens and exclude them in the market cap of bridged tokens

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 d3a54d821b60eea8a90db1c4a58cfa1d424a24ca-PR-3707

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 6 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.9%) to 64.455%

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Files with Coverage Reduction	New Missed Lines	%
lib/block_scout_web/checksum_address.ex	6	55.56%

Totals
Change from base Build 4ff75f8e5ff137786f0cf23381c47dbaf62db96e:	-0.9%
Covered Lines:	2098
Relevant Lines:	3255

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💛 - Coveralls