feat: buildkite release notes (#1910)

Adds a link to the latest version notes in the PR body, as well as a source compare link for all commits between the current version and the new version.

Closes #1876

lib/config/templates/buildkite/pr-body.hbs

-This Pull Request updates buildkite plugin {{#if repositoryUrl}}[{{{depName}}}]({{{repositoryUrl}}}){{else}}`{{{depName}}}`{{/if}} from `{{{currentVersion}}}` to `{{{newVersion}}}`.
+This Pull Request updates buildkite plugin {{#if repositoryUrl}}[{{{depName}}}]({{{repositoryUrl}}}){{else}}`{{{depName}}}`{{/if}} from `{{{currentVersion}}}` to `{{{newVersion}}}` ([release notes]({{{repositoryUrl}}}/releases/tag/{{{newVersion}}})).
+
+[Compare source commits]({{{repositoryUrl}}}/compare/{{{currentVersion}}}...{{{newVersion}}})
 
 {{#if releases.length}}
 

test/config/__snapshots__/index.spec.js.snap

@@ -31,7 +31,7 @@ Object {
       "\\\\.buildkite/.+\\\\.yml$",
     ],
     "managerBranchPrefix": "buildkite-",
-    "prBody": "This Pull Request updates buildkite plugin {{#if repositoryUrl}}[{{{depName}}}]({{{repositoryUrl}}}){{else}}\`{{{depName}}}\`{{/if}} from \`{{{currentVersion}}}\` to \`{{{newVersion}}}\`.\\n\\n{{#if releases.length}}\\n\\n{{#if schedule}}\\n**Note**: This PR was created on a configured schedule (\\"{{{schedule}}}\\"{{#if timezone}} in timezone \`{{{timezone}}}\`{{/if}}) and will not receive updates outside those times.\\n{{/if}}\\n\\n{{#if isPin}}\\n**Important**: Renovate will wait until you have merged this Pin request before creating PRs for any *upgrades*. If you do not wish to pin anything, please update your config accordingly instead of leaving this PR open.\\n{{/if}}\\n{{#if hasReleaseNotes}}\\n\\n<details>\\n<summary>Release Notes</summary>\\n\\n{{#each releases as |release|}}\\n{{#if release.releaseNotes}}\\n### [\`v{{{release.version}}}\`]({{{release.releaseNotes.url}}})\\n{{#if release.compare.url}}\\n[Compare Source]({{release.compare.url}})\\n{{/if}}\\n{{{release.releaseNotes.body}}}\\n\\n---\\n\\n{{/if}}\\n{{/each}}\\n</details>\\n{{/if}}\\n\\n{{/if}}\\n\\n{{#if hasErrors}}\\n\\n---\\n\\n# Errors\\n\\nRenovate encountered some errors when processing your repository, so you are being notified here even if they do not directly apply to this PR.\\n\\n{{#each errors as |error|}}\\n-   \`{{error.depName}}\`: {{error.message}}\\n{{/each}}\\n{{/if}}\\n\\n{{#if hasWarnings}}\\n\\n---\\n\\n# Warnings\\n\\nPlease make sure the following warnings are safe to ignore:\\n\\n{{#each warnings as |warning|}}\\n-   \`{{warning.depName}}\`: {{warning.message}}\\n{{/each}}\\n{{/if}}",
+    "prBody": "This Pull Request updates buildkite plugin {{#if repositoryUrl}}[{{{depName}}}]({{{repositoryUrl}}}){{else}}\`{{{depName}}}\`{{/if}} from \`{{{currentVersion}}}\` to \`{{{newVersion}}}\` ([release notes]({{{repositoryUrl}}}/releases/tag/{{{newVersion}}})).\\n\\n[Compare source commits]({{{repositoryUrl}}}/compare/{{{currentVersion}}}...{{{newVersion}}})\\n\\n{{#if releases.length}}\\n\\n{{#if schedule}}\\n**Note**: This PR was created on a configured schedule (\\"{{{schedule}}}\\"{{#if timezone}} in timezone \`{{{timezone}}}\`{{/if}}) and will not receive updates outside those times.\\n{{/if}}\\n\\n{{#if isPin}}\\n**Important**: Renovate will wait until you have merged this Pin request before creating PRs for any *upgrades*. If you do not wish to pin anything, please update your config accordingly instead of leaving this PR open.\\n{{/if}}\\n{{#if hasReleaseNotes}}\\n\\n<details>\\n<summary>Release Notes</summary>\\n\\n{{#each releases as |release|}}\\n{{#if release.releaseNotes}}\\n### [\`v{{{release.version}}}\`]({{{release.releaseNotes.url}}})\\n{{#if release.compare.url}}\\n[Compare Source]({{release.compare.url}})\\n{{/if}}\\n{{{release.releaseNotes.body}}}\\n\\n---\\n\\n{{/if}}\\n{{/each}}\\n</details>\\n{{/if}}\\n\\n{{/if}}\\n\\n{{#if hasErrors}}\\n\\n---\\n\\n# Errors\\n\\nRenovate encountered some errors when processing your repository, so you are being notified here even if they do not directly apply to this PR.\\n\\n{{#each errors as |error|}}\\n-   \`{{error.depName}}\`: {{error.message}}\\n{{/each}}\\n{{/if}}\\n\\n{{#if hasWarnings}}\\n\\n---\\n\\n# Warnings\\n\\nPlease make sure the following warnings are safe to ignore:\\n\\n{{#each warnings as |warning|}}\\n-   \`{{warning.depName}}\`: {{warning.message}}\\n{{/each}}\\n{{/if}}",
   },
   "bumpVersion": null,
   "circleci": Object {