https://gitlab.developers.cam.ac.uk/uis/devops/digital-admissions/pools/synchronisation-service/-/issues/166 - docs: update Digital Pooling documentation

docs: document which CamSIS envs Digital Pooling services use

docs: add link to logs for 'integration' env of Digital Pooling

docs: document how Digital Pooling services are deployed
Document how Digital Pooling follows the divisional deployment
boilerplate standard. Pipelines in service repos push images
to the meta Artifact Repository and pipelines in the deployment
project are responsible for running terraform plan & apply.

chore: add Brent's Digital Pooling Structurizr diagram

chore: format & fix links on Digital Pooling page
Apply consistent formatting to markdown and fix links to point
to locations under ...devops/digital-admissions/pools/