Fix performance of the balance changing history list loading

[vbaranov]

#1946

Should be merged after #3125

Motivation

Balance changing history list (which is under balance history chart) loading at Coin Balance History tab is very slow.

Changelog

Eliminate joining to Blocks table in the query to find the list of balance changes by finding min/max blocks in the list and interpolate blocks timestamps using those min and max numbers.

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 9fb7df04-9aea-499f-9dee-4d77c3523b74

• 3 of 27 (11.11%) changed or added relevant lines in 2 files are covered.
• 3 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.2%) to 74.897%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
apps/explorer/lib/explorer/chain.ex	0	24	0.0%

Files with Coverage Reduction	New Missed Lines	%
apps/block_scout_web/lib/block_scout_web/controllers/chain/market_history_chart_controller.ex	1	78.57%
apps/explorer/lib/explorer/chain.ex	2	75.14%

Totals
Change from base Build f94dc271-8c5a-4cda-a8b4-3d791ee6a587:	-0.2%
Covered Lines:	5833
Relevant Lines:	7788

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💛 - Coveralls