Replace existing links to the GitHub repository and files

[edhamiltonHO]

Links exist in Github documentation and in eleventy processed pages

[edhamiltonHO]

Have done first pass. Still to-do

• [x] in root, all checked

• [x] README.md - just changed links

• [x] CONTRIBUTING.md - changed links and removed reference to Snyk

• [x] in /.github - need to check all as there are absolute links to standards for writing principles and patterns etc (will change to engineering.homeoffice.gov.uk)

• [x] /docs/patterns

• [x] /docs/principles

• [x] /docs/standards

• [x] in /docs root - all checked

• [x] /docs/assets/logos - all checked

• [x] /docs/styles - all checked

• [x] in /technical-docs - all checked

• [x] in /nginx - all checked

• [x] in lib/markdown - all checked

• [x] in /helm - all checked

• [x] in /data - all checked

• [x] in /includes - all checked

• [x] in /cypress - all checked