Drop PHP 7.3 support, prepare for Renovate with reusable workflows

[ghostwriter]

Q	A
QA	yes

Description

Adding Renovate to Laminas, Mezzio repositories. https://gist.github.com/weierophinney/49ca8ae2b916d898dd3d4162b26ff41b

• Configure minimum supported PHP version
• Update composer dependencies
• Update to reusable Continuous Integration workflow
• Update to reusable Automatic Releases workflow

[ghostwriter]

Ready for review @Ocramius