Add descriptions to schemas by hand to MM resources

[upodroid]

Fixes: hashicorp/terraform-provider-google#8236

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)

pubsub: deprecated `path` field in `google_pubsub_subscription` resource as it is identical value to `id` field.

kms: deprecated `self_link` field in `google_kms_keyring` and `google_kms_cryptokey` resource as it is identical value to `id` field.

compute: deprecated `source_disk_url` field in `google_compute_snapshot`.

[modular-magician]

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

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@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 ( 5 files changed, 18 insertions(+), 12 deletions(-))
Terraform Beta: Diff ( 7 files changed, 20 insertions(+), 13 deletions(-))

[upodroid]

I looked at all the schema entries manually loaded in MM and I have a few questions:

• source_disk_link in snapshot.erb(google_compute_snapshot). This is not documented in the provider and all it seems to be doing is converting selflinks to a one with v1 in the url.
• KMS self_link also needs deprecating as it is identical to id and KMS API doesn't have self_links.

[rileykarson]

LGTM. I'm going to hold merging in case you want to deal with either of the other two fields at the same time:

• source_disk_link appears to have outputted the source_disk value from the API at some point (and source_disk did not), but is redundant with source_disk now and should be safe to deprecate. hashicorp/terraform-provider-google@50e8c65

• The KMS self_link field came from a time when we added artificial self_link fields to non-GCE resources. If it's redundant with id, that should be fine to deprecate.

[upodroid]

I'll deprecate both and open issues to remove them

[modular-magician]

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

Diff report:

Terraform GA: Diff ( 8 files changed, 25 insertions(+), 14 deletions(-))
Terraform Beta: Diff ( 9 files changed, 26 insertions(+), 14 deletions(-))

[rileykarson]

Added some minor suggestions on the deprecation notes. Can you also mark them as deprecated in the website documentation as well?

[modular-magician]

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

Diff report:

Terraform GA: Diff ( 10 files changed, 27 insertions(+), 16 deletions(-))
Terraform Beta: Diff ( 12 files changed, 29 insertions(+), 17 deletions(-))

[modular-magician]

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

Diff report:

Terraform GA: Diff ( 10 files changed, 27 insertions(+), 16 deletions(-))
Terraform Beta: Diff ( 11 files changed, 28 insertions(+), 16 deletions(-))

[upodroid]

bump