Import bridged tokens custom metadata

[vbaranov]

Motivation

Get more metadata of bridged tokens from foreign chain

Changelog

FOREIGN_JSON_RPC is introduced: JSON RPC endpoint to the foreign chain to get metadata from contract

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 eb1bf7917b8f6ac339846d39e96b97db17801b13-PR-3282

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+4.7%) to 75.64%

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Totals
Change from base Build 716aa438993f01f20c73a46988cabc14d532cebf:	4.7%
Covered Lines:	1922
Relevant Lines:	2541

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💛 - Coveralls