rebased embedr (#3511)

* skeleton of embedr service, based on bskyweb

* embedr container setup

* builds on this branch

* actual routes

* fix embedr go:embed

* tweak embedr dockerfile

* progress on embedr

* fix path params

* tweaks to build process

* try to get embedr dockerfile to install embed deps

* build this branch

* updates to match sam's output HTML

* try to unbreak embedr dockerfile

* small embedr tweak

* docker hack

* get embed.js copied over to embedr

* don't x-frame-options for embed.bsky.app

* bskyembed: remove a console.log

* use html/template for golang snippet generation

* simplify embedr API fetches

* missing file

* Rm console.log fully

---------

Co-authored-by: Dan Abramov <dan.abramov@gmail.com>

bskyweb/README.embed.md

@@ -0,0 +1,52 @@
+
+## oEmbed
+
+<https://oembed.com/>
+
+* URL scheme: `https://bsky.app/profile/*/post/*`
+* API endpoint: `https://embed.bsky.app/oembed`
+
+Request params:
+
+- `url` (required): support both AT-URI and bsky.app URL
+- `maxwidth` (optional): [220..550], 325 is default
+- `maxheight` (not supported!)
+- `format` (optional): only `json` supported
+
+Response format:
+
+- `type` (required): "rich"
+- `version` (required): "1.0"
+- `author_name` (optional): display name
+- `author_url` (optional): profile URL
+- `provider_name` (optional): "Bluesky Social"
+- `provider_url` (optional): "https://bsky.app"
+- `cache_age` (optional, integer seconds): 86400 (24 hours) (?)
+- `width` (required): ?
+- `height` (required): ?
+
+Not used:
+
+- title (optional): A text title, describing the resource.
+- thumbnail_url (optional): A URL to a thumbnail image representing the resource. The thumbnail must respect any maxwidth and maxheight parameters. If this parameter is present, thumbnail_width and thumbnail_height must also be present.
+- thumbnail_width (optional): The width of the optional thumbnail. If this parameter is present, thumbnail_url and thumbnail_height must also be present.
+- thumbnail_height (optional): The height of the optional thumbnail. If this parameter is present, thumbnail_url and thumbnail_width must also be present.
+
+Only `json` is supported; `xml` is a 501.
+
+```
+<link rel="alternate" type="application/json+oembed" href="https://embed.bsky.app/oembed?format=json&url=https://bsky.app/profile/bnewbold.net/post/abc123" />
+```
+
+
+## iframe URL
+
+`https://embed.bsky.app/embed/<did>/app.bsky.feed.post/<rkey>`
+`https://embed.bsky.app/static/embed.js`
+
+```
+<blockquote class="bluesky-post" data-lang="en" data-align="center">
+  <p lang="en" dir="ltr">{{ post-text }}</p>
+  &mdash; US Department of the Interior (@Interior) <a href="https://twitter.com/Interior/status/463440424141459456?ref_src=twsrc%5Etfw">May 5, 2014</a>
+</blockquote>
+```