Docker setup update to be compatible with Erlang OTP 23

[vbaranov]

Resolves #2852

Motivation

Update Docker setup to be compatible with Erlang OTP 23

Changelog

• install rustc for ex_keccak dependency
• python -> python3
• Postgres 12.4 -> 12.5
• Run migrations with start command even if Postgres container exists/started

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 ef0dd0a221c9f9cae094164f550aae07e02d0e36-PR-3487

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-1.2%) to 66.904%

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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%

Totals
Change from base Build c046ec07cdafe5e5480883ca86e4b7b8180767b4:	-1.2%
Covered Lines:	2064
Relevant Lines:	3085

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💛 - Coveralls