Display the database adapter name in a human-friendly way

What does this MR do?

Add a helper method to return a human-friendly name for database adapter.

• Rails Console:

  • Before:

  ❯ bin/rails c
  -------------------------------------------------------------------------------------
   GitLab:       11.9.0-pre (134df14c1c3)
   GitLab Shell: 8.7.1
   postgresql:   9.6.11
  -------------------------------------------------------------------------------------
  Loading development environment (Rails 5.0.7.1)

  • After:

  ❯ bin/rails c
  -------------------------------------------------------------------------------------
   GitLab:       11.9.0-pre (134df14c1c3)
   GitLab Shell: 8.7.1
   PostgreSQL:   9.6.11
  -------------------------------------------------------------------------------------
  Loading development environment (Rails 5.0.7.1)

• bin/rake gitlab:env:info

  • Before

  ❯ bin/rake gitlab:env:info
  
  GitLab information
  Version:  11.9.0-pre
  Revision: 64fcdd38260
  Directory:  /Users/dbalexandre/Workspace/gdk-ce/gitlab
  DB Adapter: postgres
  URL:    http://localhost:3000
  HTTP Clone URL: http://localhost:3000/some-group/some-project.git
  SSH Clone URL:  ssh://dbalexandre@localhost:2222/some-group/some-project.git
  Using LDAP: no
  Using Omniauth: yes

  • After

  ❯ bin/rake gitlab:env:info
  
  GitLab information
  Version:  11.9.0-pre
  Revision: 64fcdd38260
  Directory:  /Users/dbalexandre/Workspace/gdk-ce/gitlab
  DB Adapter: PostgreSQL
  URL:    http://localhost:3000
  HTTP Clone URL: http://localhost:3000/some-group/some-project.git
  SSH Clone URL:  ssh://dbalexandre@localhost:2222/some-group/some-project.git
  Using LDAP: no
  Using Omniauth: yes

• Admin Dashboaad:

  • Before:

  

  • After