Add "Embargo" to local KB data model and imports

• Add embargo fields to PCI in data model
  • There can be "at both the beginning and end of a coverage range" - propose these are stored separately
  • The embargo statement has a type "R" or "P"
  • The embargo statement has two parts: Units (“D” for days, “M” for months, and “Y” for years) and Length (An integer expressing the length of the embargo)
• Ensure that data entered in those fields meets KBART standard for Embargo information
• Update the JSON agreement-package import to include Embargo information
• Update KBART import to update Embargo information
• Update GOKb sync to update Embargo information
• Log situations where Embargo information does not meet KBART standard and so cannot be updated

KBART defines valid embargo data as follows:

6.6.14 Embargo
The embargo field reflects limitations on when resources become available online, generally as a result of contractual limitations established between the publisher and the content provider. Presenting this information to librarians (usually via link resolver owners) is vital to ensure that link resolvers do not generate links to content that is not yet available for users to access.

One of the biggest problems facing members of the supply chain is that multiple kinds of embargoes exist—in some cases, coverage “to one year ago” means that data from 365 days ago becomes available today, while in other cases it means that the item is not available until the end of the current calendar year.

Because of the complexities of embargoes, we recommend that the ISO 8601 date syntax should be used in this field. This is flexible enough to allow multiple types of embargoes to be described.

The following method for specifying embargoes is derived from the duration syntax in the ISO 8601 standard, making a few additional distinctions not covered in the standard. The embargo statement has three parts: type, length, and units, as described below. These three parts are written in that order in a single string with no spaces.

• Type – All embargoes involve a “moving wall,” a point in time expressed relative to the present (e.g., “12 months ago”). If access to the journal begins at the moving wall, the embargo type is “R” (defined as “recurring” in ISO 8601). If access ends at the moving wall, then the embargo type is “P” (defined as “period” in ISO 8601).
• Length – An integer expressing the length of the embargo.
• Units– The units for the number used in the “length” field, specifically “D” for days, “M” for months, and “Y” for years. For simplicity, “365D” will always be equivalent to one year, and “30D” will always be equivalent to one month, even in leap years and for months that do not have 30 days. The “units” field also indicates the granularity of the embargo, that is, how frequently the moving wall “moves.”

Examples:
• A newspaper database has a subscription model that gives customers access to exactly one year of past content. Each day, a new issue is added, and the issue that was published exactly one year ago that day is removed from the customer’s access. In this case, the embargo statement would be “R365D”, because the date of the earliest accessible issue changes each day.
• A journal has a model that gives access to all issues in the current year, starting in January. The following January, the customer loses access to all of the previous year’s issues at once, and will only be able to access issues published in the current year. In this case, we would say that the customer has access to one “calendar year” of content. The embargo statement would be “R1Y”, because the date of the earliest issue changes once a year.
• Access to all content, except the current calendar year is “P1Y”.
• Access to all content in the previous and current calendar years is “R2Y”.
• Access to all content from exactly 6 months ago to the present is “R180D”.
• Access to all content, except the past 6 calendar months is “P6M”.
In the case where there is an embargo at both the beginning and end of a coverage range, then two embargo statements should be concatenated, the starting embargo coming first. The two statements should be separated by a semicolon. For example, “R10Y;P30D” describes an archive in which the past 10 calendar years of content are available, except for the most current 30 days.