[core-v2.6.0-alpha.4, react-v2.2.5-alpha.4, vue-v2.1.5-alpha.4] : Fix - Add optionality to containerElement, format validation so accountCent…

[Adamj1232]

Description

Fixes: #1156
Add optionality to containerElement property within the accountCenter init object
Format validation so Account Center validations are close to each other and the Account Center init object use the same reference object called accountCenterInitOptions within the validation file
Bump versions

Checklist

• The version field in package.json is incremented following semantic versioning
• The box that allows repo maintainers to update this PR is checked
• I tested locally to make sure this feature/fix works
• I have run yarn type-check & yarn build to confirm there are not any associated errors
• This PR passes the Circle CI checks