[ansible/artifactory] Configure admin credentials

[bbaassssiiee]

PR Checklist

[Place an '[x]' (no spaces) in all applicable fields. Please remove unrelated fields.]

• [X] Title of the PR starts with installer/product name (e.g. [ansible/artifactory])
• [X] CHANGELOG.md updated
• [X] Variables and other changes are documented in the README.md

What this PR does / why we need it: This PR creates the initial admin password with the chosen string. It suggests using ansible-vault to encrypt it. We need it because software deployed with default passwords is a bad practice.

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #

294

Special notes for your reviewer: Credits to @eugene-krivosheyev for the initial solution.

[Logeshwarsn]

@bbaassssiiee I have added a few comments . Could you please address that ?