Transactions history chart

[vbaranov]

Origin in #2480
Closes #811
Closes #2985

Motivation

Add Transactions history chart

A new set of environment variables:

Variable	Required	Description	Default	Version	Need recompile
ENABLE_TX_STATS		Disables or enables txs per day stats gathering	false	v3.1.2+
DISABLE_EXCHANGE_RATES		Disables or enables fetching of coin price from Coingecko API	false	v3.1.2+
SHOW_PRICE_CHART		Disables or enables price and market cap of coin charts on the main page	false	v3.1.2+
SHOW_TXS_CHART		Disables or enables txs count per day chart on the main page	false	v3.1.2+
HISTORY_FETCH_INTERVAL		Interval in minutes how often to request count of txs per current day in order to display txs count per day chart on the main page	60	v3.1.2+
TXS_HISTORIAN_INIT_LAG		The initial delay in minutes in txs count history fetching in order to display txs count per day history chart on the main page	0	v3.1.2+
TXS_STATS_DAYS_TO_COMPILE_AT_INIT		Number of days for fetching of history of txs count per day in order to display it in txs count per day history chart on the main page	365	v3.1.2+

Related PR to update docs blockscout/docs#16

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 894abfaa-b76a-467d-9e27-78468e816017

• 70 of 80 (87.5%) changed or added relevant lines in 8 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.1%) to 74.943%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
apps/block_scout_web/lib/block_scout_web/controllers/chain_controller.ex	10	11	90.91%
apps/explorer/lib/explorer/chain/transaction/history/transaction_stats.ex	2	3	66.67%
apps/explorer/lib/explorer/history/process.ex	20	22	90.91%
apps/block_scout_web/lib/block_scout_web/notifier.ex	0	6	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%

Totals
Change from base Build 845910f5-cf6e-4dd9-9ccc-5d9bc05bffa0:	0.1%
Covered Lines:	5611
Relevant Lines:	7487

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💛 - Coveralls