add ability to manage firestore fields

[prodaccess]

Release Note Template for Downstream PRs (will be copied)

release-note:enhancement

I'm not sure which release-note to use. either enhancement or new-resource.

One TODO remains, which is to read the proper state of fields to compare and construct the terraform state.

I'd like to get initial reviews to make sure I am on the right track to add the ability to create Single field index via terraform

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[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, 935 insertions(+), 2 deletions(-))
Terraform Beta: Diff ( 5 files changed, 935 insertions(+), 2 deletions(-))
TF Conversion: Diff ( 1 file changed, 186 insertions(+))

[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.

@SirGitsalot, 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, 935 insertions(+), 2 deletions(-))
Terraform Beta: Diff ( 5 files changed, 935 insertions(+), 2 deletions(-))
TF Conversion: Diff ( 1 file changed, 186 insertions(+))

[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, 933 insertions(+), 2 deletions(-))
Terraform Beta: Diff ( 5 files changed, 933 insertions(+), 2 deletions(-))
TF Conversion: Diff ( 1 file changed, 186 insertions(+))

[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, 962 insertions(+), 2 deletions(-))
Terraform Beta: Diff ( 5 files changed, 962 insertions(+), 2 deletions(-))
TF Conversion: Diff ( 1 file changed, 189 insertions(+))

[nat-henderson]

@prodaccess - hi there - did you mean for this to remain a draft? If so, just notify me when you're ready for review!

[prodaccess]

Hi, thanks for checking in. Yes, I still need to fix the resource read/update part. I can create and destroy just fine, but terraform show doesn't work as expected. I got sidetracked by #3646.

[nat-henderson]

Hi there - since this has been stale for 6+ months I'm closing it, but do reopen if you ever decide to move it to ready-for-review!