Show current block template on stats

[pool2win]

We want to show the current blocktemplate being used for jobs.

The block templates changes every 10 seconds, so we might need to poll this from the node.

Assume the block template is available on disk, from database or through an API as a json object. That is, this issue doesn't require the change to p2poolv2 node to serve the block template. Instead, this issue will determine how p2poolv2 node serves the block template.

With the blocktemplate available, render it using mempool.space's block widget. They use angular so we should use the component.

The goal of the issue is

• Copy a hard coded blocktemplate into a stats page and render it. This step focuses on getting the angular component to work in a clean way. Recall, as the component upstream evolves, we will need to pull that into our stats page, so the component in our code base should be easy to upgrade by copy pasting a set of files.
• Investigate how we can now replace the hard coded blocktemplate by reading it from disk, database or websocket. That is figure out what can work easily with mempool.space's component.
• Once we have decided which is the most suitable way for us to serve the blocktemplate, change stats to read the blocktemplate using that mechanism and render the blocktemplate.
• To test stats, we will need to provide a mock/dummy service or file on disk or record in database to provide the blocktemplate that stats can render.

Once we have this done, we can then make he change in p2poolv2 node to serve the template according to what we have decided. That change will be a separate issue.