New GitHub Deprecation PR Template

[MagdalenaLarge]

As Software Developer I want have clear template for Deprecation Pull Request in GitHub So that all the future deprecations are following standardised format.

Description During the process of preparing the standardise documentation for the future releases it was identified that we need new template for the deprecation PR. Template already in https://confluence.ons.gov.uk/display/SDC/Deprecation+Implementation+and+Release+Process

Acceptance Criteria

1. Template format is agreed between Dev team
2. Template is covering all the tasks necessary to prepare deprecation PR
3. Documentation is stored in GitHub.

Visualisation/Input from UCD n/a

Linked User stories/epics

202 and #203

Technical details (optional) Need to introduce GitHub template varied parameter PR templates

MVP (optional)