## Changes
While working on the v2 of #1744, I found that:
* Template initialization first copies built-in templates to a temporary
directory before initializing them
* Reading a template's contents goes through a `filer.Filer` but is
hardcoded to a local one
This change updates the interface for reading templates to be `fs.FS`.
This is compatible with the `embed.FS` type for the built-in templates,
so they no longer have to be copied to a temporary directory before
being used.
The alternative is to use a `filer.Filer` throughout, but this would
have required even more plumbing, and we don't need to _read_ templates,
including notebooks, from the workspace filesystem (yet?).
As part of making `template.Materialize` take an `fs.FS` argument, the
logic to match a given argument to a particular built-in template in the
`init` command has moved to sit next to its implementation.
## Tests
Existing tests pass.
Adds better error message when input path is not a bundle template
before:
```
shreyas.goenka@THW32HFW6T bricks % cli bundle init ~/bricks
Error: open /Users/shreyas.goenka/bricks/databricks_template_schema.json: no such file or directory
```
after:
```
shreyas.goenka@THW32HFW6T bricks % cli bundle init ~/bricks
Error: expected to find a template schema file at /Users/shreyas.goenka/bricks/databricks_template_schema.json
```
Pieter Noordhuis
shreyas-goenka