Replace placeholders in example OC4IDS JSON file

[pindec]

The example OC4IDS JSON file contains some placeholder values that should be replaced to avoid confusion.

They include:

• Duplicate contactPoint fields for different parties (the same party/contactPoint/telephone value appears 4 times, the same party/contactPoint/faxNumber appears 3 times, duplicate uses of www.example.com across party/contactPoint/url fields)
• A placeholder for the publication policy ("https://standard.open-contracting.org/1.1/en/implementation/publication_policy/"), which could be replaced with an example.com url to indicate that publishers should publish their own policy and link to it
• Dummy identifiers for parties (e.g. party/identifier/id = "XX1234").