[Advanced Settings] Improve dirty state UI (save and cancel buttons)

[cchaos]

There are two problems that still needs to be solved on the Advanced Settings page.

1. UX of saving individual settings. It's quite cumbersome for someone to want to change more than one setting at a time, but having to hit "Save" for each individual setting.
2. UI for when the save/cancel buttons appear. When viewed at certain screen sizes, the appearance of the buttons causes the page to increase in width but not include any scrollbars and therefore can cut off the buttons entirely.

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Suggested resolution

I highly suggest that we switch to using the EuiBottomBar that will contain a "Save" and "Cancel" button that will appear once any of the fields become "dirty" and will save or cancel all dirty stated fields at once.

This will fix both problems even allowing more horizontal space usage to the fields themselves.

Example:

[elasticmachine]

Pinging @elastic/kibana-design

[elasticmachine]

Pinging @elastic/es-ui

[elasticmachine]

Pinging @elastic/kibana-app

[cjcenizal]

FYI, this is outside of the Elasticsearch UI team's purview. We just work on the apps under the "Elasticsearch" section of Management, and Dev Tools.