Move pkgdown building and deployment to GH action (#802)

Automatically build and deploy pkgdown website via GH actions. New
`pkgdown.yaml` CI workflow to build and deploy on commit to `main` or a
GH release. Deployment occurs via a new `gh-pages` branch

Also, remove the existing pkgdown website from the `main` branch, and
add the `docs/` directory to `.gitignore` to prevent it from being
re-checked in to `main`

[SC-62380](https://app.shortcut.com/tiledb-inc/story/62380)
resolves #798

.Rbuildignore

@@ -28,3 +28,4 @@
 ^codecov.yml
 ^notes.md
 ^pkgdown
+^\.github$

.github/.gitignore

@@ -0,0 +1 @@
+*.html

.github/workflows/pkgdown.yaml

@@ -0,0 +1,46 @@
+# Workflow derived from https://github.com/r-lib/actions/tree/v2/examples
+# Need help debugging build failures? Start at https://github.com/r-lib/actions#where-to-find-help
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+  release:
+    types: [published]
+  workflow_dispatch:
+
+name: pkgdown.yaml
+
+permissions: read-all
+
+jobs:
+  pkgdown:
+    runs-on: ubuntu-latest
+    # Only restrict concurrency for non-PR jobs
+    concurrency:
+      group: pkgdown-${{ github.event_name != 'pull_request' || github.run_id }}
+    env:
+      GITHUB_PAT: ${{ secrets.GITHUB_TOKEN }}
+    permissions:
+      contents: write
+    steps:
+      - uses: actions/checkout@v4
+      - uses: r-lib/actions/setup-pandoc@v2
+      - uses: r-lib/actions/setup-r@v2
+        with:
+          use-public-rspm: true
+      - uses: r-lib/actions/setup-r-dependencies@v2
+        with:
+          extra-packages: any::pkgdown, local::.
+      - name: Build vignettes
+        run: cd vignettes/ && make
+      - name: Build site
+        run: pkgdown::build_site_github_pages(new_process = FALSE, install = FALSE)
+        shell: Rscript {0}
+      - name: Deploy to GitHub pages
+        if: github.event_name != 'pull_request'
+        uses: JamesIves/github-pages-deploy-action@v4.5.0
+        with:
+          clean: false
+          branch: gh-pages
+          folder: docs

.gitignore

@@ -7,10 +7,15 @@
 TileDB-R.Rproj
 # Example code in package build process
 *-Ex.R
+# pkgdown artifacts
+docs/
 # Build artifacts
 src/*.o
+src/*/*.o
 src/*.so
 src/*.dll
+inst/lib/*/*.dll
+inst/tiledb
 # Output files from R CMD build
 /*.tar.gz
 # Output files from R CMD check