Account: derive Auth0 logout urls from existing envs

[vbaranov]

Motivation

Currently, in order to setup Account functionality, Blockscout requires:

export ACCOUNT_AUTH0_LOGOUT_URL=https://auth0_domain/v2/logout
export ACCOUNT_AUTH0_LOGOUT_RETURN_URL=explorer_protocol://explorer_host:explorer_port/explorer_path/auth/logout

to be set.

However,

• we already defined auth0_domain in ACCOUNT_AUTH0_DOMAIN
• explorer_protocol://explorer_host:explorer_port/explorer_path is already can be constructed via BlockScoutWeb.APIDocsView.blockscout_url() function.

Changelog

Remove redundant

• ACCOUNT_AUTH0_LOGOUT_URL
• ACCOUNT_AUTH0_LOGOUT_RETURN_URL
  environment variables.

Docs update in blockscout/docs#144.
Frontend deployments update blockscout/frontend#785.
Deployment values update https://github.com/blockscout/deployment-values/pull/38.

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