This feature was added when an internal fixed value of `20` was in use. It was configurable via graphql query parameters as well as overriding the default value in the plugin config, but this was not obvious as no default was set.

As the default is `20`, it has been relocated to the plugin defaults, and the redundant method to get the `base64Width` value has been removed(this was implemented before the plugin defaults and options were refactored out to a separate file).

Using a default of `false` is a bit misleading as the expected values are `jpg`,`png` and `webp`, not `true`. The empty string is a falsey value, serving the same purpose. This matches the defaults for similar properties in general args.

Additionally updates the docs to show the actual default values and missing options for plugin config options, as these lacked public documentation.

Documents these two parameters for graphql (and their global default override option equivalents via plugin config).

`args` is a parameter, it should not have it's props modified, referencing the `options` object instead where `toFormat` may be modified.

Rename the `forceBase64Format` variable to `changedBase64Format`. Should be less likely to imply a boolean, and isn't necessarily the same value as `forceBase64Format` stored on the `pluginOptions`.

`healOptions()` needed an update to pull in the `base64Width` default as fallback.

base64 tests also needed modifications to avoid caching from calling `base64()` directly instead of via `fixed()` and `fluid()` methods which would invalidate cache and set `width` prop to `base64Width`.

Important for transparent images like PNG when converted to base64 image format like JPG where transparency is not supported.

Test is fairly basic relying on snapshot but should be sufficient to indicate if something goes wrong. Could possibly benefit with tests on fluid/fixed where the actual bug was from them not passing the option down.