feat: update to v1 protos

[mikelehen]

Update the nodejs-firestore client to use the v1 protos and endpoint. Mostly this is a no-op, though I did have to tweak the way we serialize empty document paths because the backend now requires /project/[project]/database/[database]/documents for empty document paths instead of /project/[project]/database/[database]

The v1beta1 gapic client is preserved for now and can still be used, but the manually-curated API uses v1.

[JustinBeckwith]

LGTM w/ a few nits.

1. This file shows up in the change list: dev/protos/google/firestore/v1beta1/.DS_Store. Thinking that we want to make sure all .DS_Store files are ignored and removed. It's ok to do this in a follow up PR.
2. Are there any known breaking changes for consumers of the package? In the move to v1beta1, did we change/update any APIs in a breaking way? It would be really good to call these out in the description of the PR if so.
3. Should we still be shipping the dev/protos/google/firestore/v1beta1/ directory at all?

[mikelehen]

@JustinBeckwith Thanks!

1. Good idea. Added to .gitignore.
2. For the most part, there are no breaking changes (or API changes of any kind). Switching to v1 is basically just an implementation detail. The one caveat is that the backend has made a tweak to its error handling in v1 such that writes failing due to contention will fail with error code ABORTED instead of error code UNAVAILABLE. So if any user had conditional retry logic that differentiated these cases, it could break. If you know of a good way to call this out, let me know. Else, I'm not expecting it to affect many users.
3. My expectation was that we should not keep the v1beta1 directory (and so it's removed in this PR). If you disagree, let me know.

[JustinBeckwith]

@crwilcox @jadekler Are we removing the v1beta1 library in other languages?

[jeanbza]

@JustinBeckwith We decided not to. @mikelehen could you leave the v1beta1 gapic as-is, and just switch the manual to using v1? This helps users currently relying on the beta (because they remain unbroken for a little while longer), but mostly just makes the process a bit more seamless.

[mikelehen]

I can undelete dev/src/v1beta1 (and dev/protos/google/firestore/v1beta/ too?) but I'm unclear what benefit this provides. We have to delete it before we go 1.x, right? And so if users depend on it directly, they'll need to stick with a 0.x version.

[jkwlui]

blocking this until we bring back v1beta1 back in.

[mikelehen]

@JustinBeckwith Per discussions, I've updated this PR to keep the v1beta1 gapic client and expose both v1beta1 and v1 gapic clients to developers, but the manual SDK uses v1 internally.

@kinwa91 The docs check you added in #511 is failing because of two broken links that came from the v1 protos. I see you added steps to synth.py to automatically fix them, but when I re-run synth.py I'm actually seeing it revert your changes to .kokoro/docs.sh. Am I doing something wrong?

[mikelehen]

I went ahead and checked in just the proto changes necessary to make CI pass, but I had to revert some of the other changes synth.py made.

[mikelehen]

@kinwa91 v1beta1 has been revived. Can you approve? Thanks!

[jkwlui]

synthtool hasn't been released to reflect the changes to docs.sh. I will cut a release today. LGTM