Link nested types in resource documentation pages

[juliocc]

This PR add links to nested data types within a resource's documentation page, simplifying navigation for complex resources with multiple nested types.

Format was tested against Terraform's doc preview tool and the syntax works as expected.

If this PR is for Terraform, I acknowledge that I have:

• Searched through the issue tracker for an open issue that this either resolves or contributes to, commented on it to claim it, and written "fixes {url}" or "part of {url}" in this PR description. If there were no relevant open issues, I opened one and commented that I would like to work on it (not necessary for very small changes).
• Generated Terraform, and ran make test and make lint to ensure it passes unit and linter tests.
• Ensured that all new fields I added that can be set by a user appear in at least one example (for generated resources) or third_party test (for handwritten resources or update tests).
• Ran relevant acceptance tests (If the acceptance tests do not yet pass or you are unable to run them, please let your reviewer know).
• Read the Release Notes Guide before writing my release note below.

Release Note Template for Downstream PRs (will be copied)

provider: Added links to nested types documentation within a resource 

[modular-magician]

Oops! It looks like no changelog entry is attached to this PR. Please include a release note block in the PR body, as described in https://github.com/GoogleCloudPlatform/magic-modules/blob/master/.ci/RELEASE_NOTES_GUIDE.md:

```release-note:TYPE
Release note
```

[modular-magician]

Hello! I am a robot who works on Magic Modules PRs.

I have detected that you are a community contributor, so your PR will be assigned to someone with a commit-bit on this repo for initial review.

Thanks for your contribution! A human will be with you soon.

@rileykarson, please review this PR or find an appropriate assignee.

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 148 files changed, 1857 insertions(+), 1857 deletions(-))
Terraform Beta: Diff ( 150 files changed, 1859 insertions(+), 1860 deletions(-))

[rileykarson]

Thanks @juliocc! This is very useful.