Feature/tool for importing/exporting ad layer config between sites

[jakewrfoster]

Overview:

There is no way presently to easily import/export ad server and ad layer configurations between environments. Considering that these configuration options are often needed to be identical between testing environments and production environments, an admin dashboard tool/feature for this purpose would streamline a lot of effort and remove complexity/complication for the maintenance of ad layer configurations across multiple environments.

Proposed User Story:

As an editor/maintainer of an ad layers implementation, I should be able to export and import ad layer configuration options to and from other sites.

Proposed MVP:

• [ ] Add an additional "Import/Export" submenu page to the Ad Layers menu option
• [ ] An option to export all ad server configuration
• [ ] An option to export all ad layer configuration (this would require taxonomy terms to exist in parity between environments)
• [ ] Export entire ad layer configuration (layers and server settings)
• [ ] Import configuration options (since this process needs to be done in a specific order - i.e. layers can't be created without first having ad units created - the tool/feature should be smart enough to determine what is being imported and in what order it needs to happen)

Implementation ideas:

• This could perhaps leverage custom REST endpoints. (see #54?)
• This should be fully functional from within the WP dash

[mboynes]

Lots of prior art for this in https://github.com/alleyinteractive/options-importer/blob/master/options-importer.php