Searching by verified contract name

[vbaranov]

Closes #2661

Motivation

Adds the ability to search by verified contract name

Changelog

• search_contract function which queries contracts
• extend token_autocomplete with fallback to search contracts

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 112ef4e6-ae81-435d-8e17-b137807d5e59

• 4 of 6 (66.67%) changed or added relevant lines in 2 files are covered.
• 3 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.04%) to 75.051%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
apps/explorer/lib/explorer/chain.ex	1	3	33.33%

Files with Coverage Reduction	New Missed Lines	%
apps/explorer/lib/explorer/chain.ex	1	77.83%
apps/block_scout_web/lib/block_scout_web/controllers/chain/market_history_chart_controller.ex	2	71.43%

Totals
Change from base Build 3db08de4-e97e-4877-96c7-a8823544f390:	-0.04%
Covered Lines:	5514
Relevant Lines:	7347

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💛 - Coveralls