docs: documentation update and how it's generated

[Awlie]

• added descriptions to resources in code for auto-generated docs
• removed per-resource templates and added baseline ones
  • no more duplicating and adjusting template files and introducing copy paste errors
• changed example structure so defaults in templates work out of the box (like .HasExample, .ExampleFile, .HasImport, .ImportFile)
  • formatted examples and fixed some spelling errors
  • added 3 imports
• added imports, where it's declared in the code. I'm not 100% sure that it's correct, but should be
• updated docs plugin to latest version
• added subcategories in YAML Frontmatter. These are automatically generated through the description in code and the new templates
  • This allows us to define resources descriptions with My Subcategory --- The description of my resource and have the subcategory and description correctly filled in. It also works if people don't provide a subcategory, in that case, it will just populate the description.
    The only caveat is that people can't write --- in their description (or if we do, we should change this string to one that we will never write in our descriptions).
• fixed some spelling errors
• fixed md-page of cancom_ipam_instance, which had the description of another resource
• added deprecated flag to a deprecated attribute of a resource (at least the description says so (resourceServiceUser.session_hash)

biggest change is for iam_policy.md, where i moved most of the text into the policy description, so that the information of the advanced usage is still there.

[Awlie]

in 619ac4b I migrated the new resource to the new proposed docs format

i also have some propositions to the descriptions of a few attributes, but i want to talk to CLR first

[Awlie]

@roehlc You wanted to be tagged ;)
i adjusted some descriptions in 2ce9dee

[atddo]

Nice work @Awlie !