Add guides for labels and annotations

[zli82016]

Add the introduction to the new labels and annotations models and will add more details later.

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).
• 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).
• Generated Terraform providers, and ran make test and make lint in the generated providers to ensure it passes unit and linter tests.
• Ran relevant acceptance tests using my own Google Cloud project and credentials (If the acceptance tests do not yet pass or you are unable to run them, please let your reviewer know).
• Read Write release notes before writing my release note below.

Release Note Template for Downstream PRs (will be copied)

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

Terraform GA: Diff ( 1 file changed, 18 insertions(+))
Terraform Beta: Diff ( 1 file changed, 18 insertions(+))

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

Terraform GA: Diff ( 1 file changed, 22 insertions(+))
Terraform Beta: Diff ( 1 file changed, 22 insertions(+))

[c2thorn]

This is a provider-level change, so please but it slightly lower in the

Provider section

You can then remove the example where it says "Provider-level change example header"

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

Terraform GA: Diff ( 1 file changed, 30 insertions(+))
Terraform Beta: Diff ( 1 file changed, 30 insertions(+))

[zli82016]

Thanks so much for the comments.

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

Terraform GA: Diff ( 1 file changed, 30 insertions(+))
Terraform Beta: Diff ( 1 file changed, 30 insertions(+))

[c2thorn]

Section looks much better, thank you for adding clarifications! Can we move the entire section below the ## Provider line on line 119? Then delete the

Provider-level change example header

Description of the change and how users should adjust their configuration (if needed).

lines?

[zli82016]

Section looks much better, thank you for adding clarifications! Can we move the entire section below the ## Provider line on line 119? Then delete the

Provider-level change example header

Description of the change and how users should adjust their configuration (if needed).

lines?

Done.

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

Terraform GA: Diff ( 1 file changed, 28 insertions(+), 2 deletions(-))
Terraform Beta: Diff ( 1 file changed, 28 insertions(+), 2 deletions(-))

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

Terraform GA: Diff ( 1 file changed, 28 insertions(+), 2 deletions(-))
Terraform Beta: Diff ( 1 file changed, 28 insertions(+), 2 deletions(-))