#5947 - roll up bulk asset checkout email

[marcusmoore]

Currently, checking out multiple assets via the bulk checkout feature would result in individual emails being sent for each asset that was included in the checkout. This PR changes that behavior by sending one email that contains all assets that were checked out.

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I attempted to make the resulting email as readable as possible so the new BulkAssetCheckoutMail itself does a lot of work to "bundle" up groups of assets.

• If all of the assets checked out are from the same category then the EULA for that category is displayed once
• If there are multiple assets from categories then the assets are grouped by category and their EULAs displayed at the end of each section.
• The prompt to "click to accept" is dynamic and only appears if one or more of the assets require acceptance.

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A few examples

Assets not requiring acceptance:

"Bulk" checking out a single asset:

Checking out assets where some items require acceptance:

Note that the last category "Displays" do not have a EULA so it is not displayed.

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Technical

Here are some notes on how this is technically implemented:

• Introduces a new event, CheckoutablesCheckedOutInBulk, and listener for that event.
  • The logic in here is similar to the existing CheckoutableListener but I separated it out since we're now dealing with an array of items and I didn't want to add a bunch of conditionals into the existing class.
• I'm using (abusing?) the Context facade to facilitate some code paths by adding bulk_asset_checkout to the request's context in the controller layer and checking for that context in the existing CheckoutableListener to avoid sending individual notifications.
  • This approach was used to avoid making the CheckoutableListener more complex than it already is.
• The new listener checks to see if notifications should be sent by seeing if any assets that were checked out have a EULA, requires acceptance, or have a category set to always send the email. If any of those conditions is true for one or more assets that were checked out then then the notification including all items is sent.

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Additional notes

• Webhooks still behave the same and are sent individually for each asset.
• Subject line is "Assets checked out" unless someone only selected one asset to be "bulk" checked out. If that is the case then the subject line is "Asset checked out: {asset_tag}"
• Images are not included in the email

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Partially addresses #5947 (sends one email for the entire bulk checkout instead of individual emails for each asset). If acceptance is required the user will still need to accept each asset individually.

[marcusmoore]

@snipe you rightfully mentioned that checking out items from different categories with long EULAs might trigger some truncation or character limit.

Can you look at my overall approach in this PR and let me know if it is worth continuing down this path? If so, I'm tentatively thinking I can account for this by limiting the number of categories being sent per email and potentially including logic around EULA length.