Replace 'storage_method' with 'tags'

Problem/Motivation

In #3013279: Add ability to filter list of keys based on key storage_method, storage_method has been added to the KeyProvider plugin definition. The reason was to allow better classification of plugins. However, this definition key has no other API role, it's just metadata. But it also limits the possibility to more complex classifications.

Steps to reproduce

None.

Proposed resolution

• Replace single-value storage_method definition key with a multi-string tags definition entry.
• Deprecate storage_method definition entry.
• Deprecate the key_select element #key_filters var storage_method option, in favour of a multi-value tags option.
• Adapt Drush command options

Remaining tasks

None.

User interface changes

None.

API changes

None.

Data model changes

KeyProvider plugin definition will contain a multi-string tags entry while using storage_method is deprecated.