Code changes from new metadata spec: back end

[seanprivett]

See https://docs.google.com/spreadsheets/d/1O1EjO96lyqDbyuzFWU8SNBky3b7tKM8dccZVS7-_t9g/edit#gid=1846443805

and the previous spike https://github.com/ministryofjustice/find-moj-data/issues/363

Purpose

We are adding new custom properties to Datahub that will come from DBT metadata. These will be used render the contact/where to access panel on the details page.

field name	description	example
dc_slack_channel_name	The name of a slack channel to be used as a contact point for users of the catalogue service, including the leading '#'. Note: this is not the same as the owner channel for notifications.	#data-engineering
dc_slack_channel_url	The URL to the slack channel	https://moj.enterprise.slack.com/archives/C8X3PP1TN
dc_where_to_access_dataset	An enum representing how the data can be accessed by end users. For DBT, this always defaults to AnalyticalPlatform.	AnalyticalPlatform

Required changes

• [x] Extend our metadata model to include these custom properties
• [x] Ensure these 3 attributes are passed back to the frontend
• [x] Ensure the metadata documentation page renders correctly
• [x] Ensure any references to where_to_access_dataset use the new prefixed property name

[tom-webber]

Ensure the metadata documentation page renders correctly

The Field in the metadata should reflect the name of the field when snake case, but currently capitalises with spaces