[Docs] Update merge workflow to push generated artifacts to sdk-docs …

…repo (#228)

## Problem
(These are basically the same changes as the TypeScript client, PR info
is the same: pinecone-io/pinecone-ts-client#146)

The current flow for building and deploying documentation for SDK
clients takes place within each repository. Currently, `merge` workflows
handle the docs build step, and pushing the contents of the generated
`/docs` folder to a specific branch for each client: `gh-pages`. This
branch is then used as the deployment source for GitHub pages.

There are several issues intrinsic in this:
- We have to manage each CI configuration and deployment on a per-repo
basis.
- Applying custom sub-domains to our GitHub pages instances is
difficult, and we would need to define a specific sub-domain for each
repo.
- We're unable to share resources or assets across docs pages without
duplicating things in each repo.

## Solution
Instead of having the CI workflows push documentation artifacts to a
local branch, we can instead centralize our SDK documentation in a
specific repo and allow workflows to commit docs updates directly to
this repo. This allows us to deploy all our SDK documentation via one
GitHub pages configuration. This also allows us to centralize all of our
generated documentation, which could be useful in the future where we
may move to a centralized docs-hosting solution that all the SDK repos
need to feed into.

The changes in this PR are relatively small, and there was some
pre-setup outside these changes:

### Pre-Setup
- Create new `pinecone-io/sdk-docs` private repo to house generated
documentation artifacts.
- Add SSH deploy keys to `sdk-docs` and source repos
(`pinecone-ts-client`, `pinecone-python-client`) to allow writing to the
`sdk-docs` repo.
[Documentation](https://cpina.github.io/push-to-another-repository-docs/setup-using-ssh-deploy-keys.html#setup-ssh-deploy-keys)
on this step. It's recommended to use SSH deploy keys over a GitHub PAT
token.
- SSH secrets within client repos are titled `SSH_DEPLOY_KEY`.

### This PR 
- Update `merge` workflow to use the
`github-action-push-to-another-repository` action. [Action
documentation](https://cpina.github.io/push-to-another-repository-docs/overview.html)

## Type of Change
- [X] Infrastructure change (CI configs, etc)

## Test Plan
I should have all the prerequisites set up to allow our CI workflow to
push directly to `sdk-docs`. For this change we can merge and verify
that the resulting `/docs` folder was correctly pushed to
`sdk-docs/typescript`.

I tested the structure of the repo and publishing via GitHub pages in a
personal repo:
https://github.com/austin-denoble/test-docs
- Python - https://austin-denoble.github.io/test-docs/python
- Typescript - https://austin-denoble.github.io/test-docs/typescript

.github/workflows/merge.yaml

@@ -16,10 +16,15 @@ jobs:
       - name: Generate pdoc documentation
         uses: ./.github/actions/build-docs
 
-      - name: Deploy documentation to gh-pages
-        uses: s0/git-publish-subdir-action@develop
+      - name: Push documentation artifacts to sdk-docs
+        uses: cpina/github-action-push-to-another-repository@main
         env:
-          REPO: self
-          BRANCH: gh-pages
-          FOLDER: docs
-          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          SSH_DEPLOY_KEY: ${{ secrets.SSH_DEPLOY_KEY }}
+        with:
+          source-directory: docs
+          destination-github-username: pinecone-io
+          destination-repository-name: sdk-docs
+          user-email: clients@pinecone.io
+          target-branch: main
+          target-directory: python
+          commit-message: 'Python: automated documentation build - pinecone-python-client merge SHA: ${{ github.sha }}'