Actualize Docker setup

[vbaranov]

Motivation

Actualize Docker setup with the latest set of ENV vars for Blockscout application

Changelog

• add all supported environment variables to Makefile
• increase the version of Elixir Docker image up to 1.9.1
• increase the version of Postgres Docker image up to 10.10
• add mix phx.digest command to Docker file in order to build front-end static assets
• remove dropping of DB on the start of the container since it is not safe operation (ideally, it should be a separate command to drop database)

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 8d38a414-89cc-48e2-9b29-e95b6b87c7e8

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.01%) to 75.234%

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

Totals
Change from base Build e57ca067-7f88-4266-a8e4-0de24447fcce:	-0.01%
Covered Lines:	5377
Relevant Lines:	7147

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💛 - Coveralls