Add Usercentrics CMP (cookie consent + GDPR compliance)

[ulyanas]

Some organizations require Usercentrics CMP (cookie consent + GDPR compliance) to be integrated into Blockscout frontend to comply with global user privacy regulations.

The integration should be done via a hosted js.

<script
  src="{{ usercentrics_bundle_url }}"
  async
  data-ruleset-id="{{ usercentrics_ruleset_id }}"
  id="XXX"
  key="XXX">
</script>

The variables should be set via front-end config.

Usercentrics CMP docs:
https://support.usercentrics.com/hc/en-us/articles/20056744119196-Direct-implementation-guide

https://usercentrics.com/docs/web/v3/