Update CI configurations and Dockerfile

[abitmore]

Main changes:

• Remove .travis.yml and related files
• Update dependency versions used in Github Actions
  • actions/checkout@v2 -> v3
  • actions/cache@v2 -> v3
  • docker/setup-buildx-action@v1 -> v2
  • docker/build-push-action@v2 -> v3
  • docker/login-action@v1 -> v2
  • docker://elasticsearch:7.17.5 -> 7.17.7
  • CURL_VERSION: 7.67.0 -> 7.86.0
  • OPENSSL_VERSION: 1.1.1d -> 1.1.1q
• Run sonar-scan workflow with Ubuntu 20.04 instead of ubuntu-latest because ubuntu-latest will point to Ubuntu 22.04 which we don't support yet
• Use GITHUB_REF_NAME variable provided by Github instead of rlespinasse/github-slug-action
• Update Docker base image to phusion/baseimage:focal-1.2.0, and do apt-get upgrade at build time, and do not complain if /etc/bitshares exists already.

[sonarcloud[bot]]

Kudos, SonarCloud Quality Gate passed!   

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