Update IFrame app with difference between simple standalone and MVD standalone mode

[DivergentEuropeans]

Proposed changes

The title is pretty good. It also fixes small UI bug where we couldn't do something in standalone mode (dataservice request send) that we actually can do no problem

This PR depends upon the following PRs: https://github.com/zowe/zlux-app-manager/pull/507

Type of change

Please delete options that are not relevant.

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)

PR Checklist

Please delete options that are not relevant.

• [ ] If the changes in this PR are meant for the next release / mainline, this PR targets the "staging" branch.
• [ ] My code follows the style guidelines of this project (see: Contributing guideline)
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] Relevant update to CHANGELOG.md
• [ ] My changes generate no new warnings

Testing

https://localhost:7558/ZLUX/plugins/org.zowe.zlux.bootstrap/web/?pluginId=org.zowe.zlux.sample.iframe&showLogin=true&windowManager=old

https://localhost:7558/ZLUX/plugins/org.zowe.zlux.bootstrap/web/?pluginId=org.zowe.zlux.sample.iframe&showLogin=true&windowManager=mvd

https://localhost:7558/ZLUX/plugins/org.zowe.zlux.bootstrap/web/?