Rename env vars related for the integration with microservices and footer env vars

[vbaranov]

Motivation

Rename env vars related to integration with microservices

Changelog

Add common MICROSERVICE_ prefix for env vars related to microservices

RUST_VERIFICATION_SERVICE_URL -> MICROSERVICE_SC_VERIFIER_URL
ENABLE_RUST_VERIFICATION_SERVICE -> MICROSERVICE_SC_VERIFIER_ENABLED
VISUALIZE_SOL2UML_SERVICE_URL -> MICROSERVICE_VISUALIZE_SOL2UML_URL
VISUALIZE_SOL2UML_ENABLED -> MICROSERVICE_VISUALIZE_SOL2UML_ENABLED
SIG_PROVIDER_SERVICE_URL -> MICROSERVICE_SIG_PROVIDER_URL
SIG_PROVIDER_ENABLED -> MICROSERVICE_SIG_PROVIDER_ENABLED

2. ENABLE_ prefix to _ENABLED suffix:

ENABLE_SOURCIFY_INTEGRATION -> SOURCIFY_INTEGRATION_ENABLED
CACHE_ENABLE_TOTAL_GAS_USAGE_COUNTER -> CACHE_TOTAL_GAS_USAGE_COUNTER_ENABLED
FOOTER_ENABLE_FORUM_LINK -> FOOTER_FORUM_LINK_ENABLED
ENABLE_TXS_STATS -> TXS_STATS_ENABLED

3. Env vars for footer have FOOTER_ prefix

LINK_TO_OTHER_EXPLORERS -> FOOTER_LINK_TO_OTHER_EXPLORERS
OTHER_EXPLORERS -> FOOTER_OTHER_EXPLORERS
LOGO_FOOTER -> FOOTER_LOGO

Docs update in blockscout/docs#137
Frontend test deployments update in blockscout/frontend#738
CI-CD deployment update blockscout/blockscout-ci-cd#70
Deployment values update in https://github.com/blockscout/deployment-values/pull/31

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

[ghost]

Good job