Composite market cap for xDai: TokenBridge + OmniBridge

[vbaranov]

Motivation

xDai market cap is currently comprised from xDai minted with TokenBridge and assets bridged from Mainnet by means of OmniBridge. We should account both in market cap on the main page. Currently, only TokenBridge is accounted.

Changelog

BRIDGE_MARKET_CAP_UPDATE_INTERVAL - environment variable introduced.

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 e728afc227aeadcff49b7f09f3299f173f8db175-PR-3293

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 19 unchanged lines in 3 files lost coverage.
• Overall coverage increased (+6.5%) to 75.578%

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Files with Coverage Reduction	New Missed Lines	%
lib/block_scout_web/controllers/chain/market_history_chart_controller.ex	2	71.43%
lib/block_scout_web/controllers/chain_controller.ex	5	86.49%
lib/block_scout_web/views/chain_view.ex	12	14.29%

Totals
Change from base Build a3282e8af436a7249f8af856d29aeb7ee0fa638c:	6.5%
Covered Lines:	1928
Relevant Lines:	2551

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💛 - Coveralls