MQE-2203: Create CHANGELOG.MD entry for 3.0.0

[soumyau]

consolidated change log for 3.0.0

Description

Fixed Issues (if relevant)

1. magento/magento2-functional-testing-framework#<issue_number>: Issue title
2. ...

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/verification tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)
• Changes to Framework doesn't have backward incompatible changes for tests or have related Pull Request with fixes to tests

[coveralls]

Coverage remained the same at 56.031% when pulling db284aa on MQE-2203 into c0255ee on develop.

[jilu1]

@soumyau
There are a lot of moving contents in this PR. It's not easy to tell if everything is accounted for. Spot check a few and they look good.

@okolesnyk
Since you requested this, do you like the idea to have to 3.0.0 as top level heading and keep sub heading like RC1, RC2, etc without changing the major contents?

[soumyau]

@soumyau
There are a lot of moving contents in this PR. It's not easy to tell if everything is accounted for. Spot check a few and they look good.

@okolesnyk
Since you requested this, do you like the idea to have to 3.0.0 as top level heading and keep sub heading like RC1, RC2, etc without changing the major contents?

@jilu content is intact, sequence may have changed.