configure Antora and CI workflow to support partial build (single version)

- upgrade to Antora 3.2.0-alpha.2
- upgrade release-line-extension to 1.0.0-alpha.2
- add atlas-extension
- add local autoconfig-partial-build extension
- configure deploy-docs.yml workflow to detect and set up partial build
- configure publish-docs.sh script to sync partial build

lib/antora/extensions/autoconfig-partial-build.js

@@ -0,0 +1,55 @@
+'use strict'
+
+const execFile = require('node:util').promisify(require('node:child_process').execFile)
+const { promises: fsp } = require('node:fs')
+
+module.exports.register = function () {
+  if (!process.env.BUILD_REFNAME) return
+
+  this.once('playbookBuilt', async ({ playbook }) => {
+    const { concat: get } = this.require('simple-get')
+    const asciidocAttrs = ((playbook.asciidoc ||= {}).attributes ||= {})
+    const siteManifestUrl = asciidocAttrs['primary-site-manifest-url'] || `${playbook.site.url}/site-manifest.json`
+    const siteManifestData = await (siteManifestUrl.startsWith('https://')
+      ? download(get, siteManifestUrl)
+      : fsp.readFile(siteManifestUrl)
+    ).then(JSON.parse)
+    let { BUILD_REFNAME: refname, BUILD_VERSION: version } = process.env
+    const isBranch = /[a-z]$/.test(refname)
+    if (!version) {
+      const repoUrl = await execFile('git', ['remote', 'get-url', 'origin']).then(({ stdout: output }) => output.trim())
+      const propertiesUrl = `${repoUrl.replace('github.com', 'raw.githubusercontent.com')}/${refname}/gradle.properties`
+      version = await download(get, propertiesUrl)
+        .then((contents) => contents.toString().split('\n').find((it) => it.startsWith('version='))?.slice(8))
+    }
+    if (isBranch && version.endsWith('-SNAPSHOT')) version = version.slice(0, -9)
+    const versionsInManifest = siteManifestData.components.ROOT.versions
+    if (!(version in versionsInManifest && isBranch === !!versionsInManifest[version].prerelease)) {
+      const category = require('path').basename(module.id, '.js')
+      this.getLogger(category).info(`version ${version} not previously built; reverting to full build`)
+      return
+    }
+    Object.assign(
+      playbook.content.sources[0],
+      isBranch ? { branches: [refname], tags: [] } : { branches: [], tags: [refname] }
+    )
+    Object.assign(
+      asciidocAttrs,
+      { 'primary-site-url': '.', 'primary-site-manifest-url': siteManifestUrl }
+    )
+    this.updateVariables({ playbook })
+  })
+}
+
+function download (get, url) {
+  return new Promise((resolve, reject) =>
+    get({ url }, (err, response, contents) => {
+      if (err) reject(err)
+      if (response.statusCode !== 200) {
+        const message = `Response code ${response.statusCode} (${response.statusMessage})`
+        return reject(Object.assign(new Error(message), { name: 'HTTPError' }))
+      }
+      resolve(contents)
+    })
+  )
+}