Create client registration spec draft ("Client Registration")

[daniel-utilityapi]

This is the specification (CDSC-WG1-02) describing how clients (e.g. companies wanting to request data from customers) can register with utility servers in to use the utility's offered capabilities (e.g. access to customer data via OAuth).

• [x] Write summary overview with example
  • Draft: https://github.com/daniel-utilityapi/Customer-Data/blob/main/website/specs/cdsc-wg1-02/overview.md
  • Render: https://daniel-utilityapi.github.io/Customer-Data/specs/cdsc-wg1-02/overview
• [x] Review summary overview and example with working group
• [x] Write specification draft
  • Source: https://github.com/daniel-utilityapi/Customer-Data/blob/issue_16_client_registration/specifications/cdsc-wg1-02.md
  • Render: https://daniel-utilityapi.github.io/Customer-Data/specs/cdsc-wg1-02
• [x] Open pull request for specification draft
• [ ] Review pull request with working group
• [ ] Update based on feedback
• [ ] Merge when consensus is obtained