feat: remote taskfiles (HTTP) (#1152)

* feat: remote taskfiles over http

* feat: allow insecure connections when --insecure flag is provided

* feat: better error handling for fetch errors

* fix: ensure cache directory always exists

* fix: setup logger before everything else

* feat: put remote taskfiles behind an experiment

* feat: --download and --offline flags for remote taskfiles

* feat: node.Read accepts a context

* feat: experiment docs

* chore: changelog

* chore: remove unused optional param from Node interface

* chore: tidy up and generalise NewNode function

* fix: use sha256 in remote checksum

* feat: --download by itself will not run a task

* feat: custom error if remote taskfiles experiment is not enabled

* refactor: BaseNode functional options and simplified FileNode

* fix: use hex encoding for checksum instead of b64

docs/docs/experiments/remote_taskfiles.md

@@ -0,0 +1,81 @@
+---
+slug: /experiments/remote-taskfiles/
+---
+
+# Remote Taskfiles
+
+- Issue: [#1317][remote-taskfiles-experiment]
+- Environment variable: `TASK_X_REMOTE_TASKFILES=1`
+
+This experiment allows you to specify a remote Taskfile URL when including a
+Taskfile. For example:
+
+```yaml
+version: '3'
+
+include:
+  my-remote-namespace: https://raw.githubusercontent.com/my-org/my-repo/main/Taskfile.yml
+```
+
+This works exactly the same way that including a local file does. Any tasks in
+the remote Taskfile will be available to run from your main Taskfile via the
+namespace `my-remote-namespace`. For example, if the remote file contains the
+following:
+
+```yaml
+version: '3'
+
+tasks:
+  hello:
+    silent: true
+    cmds:
+      - echo "Hello from the remote Taskfile!"
+```
+
+and you run `task my-remote-namespace:hello`, it will print the text: "Hello
+from the remote Taskfile!" to your console.
+
+## Security
+
+Running commands from sources that you do not control is always a potential
+security risk. For this reason, we have added some checks when using remote
+Taskfiles:
+
+1. When running a task from a remote Taskfile for the first time, Task will
+   print a warning to the console asking you to check that you are sure that you
+   trust the source of the Taskfile. If you do not accept the prompt, then Task
+   will exit with code `104` (not trusted) and nothing will run. If you accept
+   the prompt, the remote Taskfile will run and further calls to the remote
+   Taskfile will not prompt you again.
+2. Whenever you run a remote Taskfile, Task will create and store a checksum of
+   the file that you are running. If the checksum changes, then Task will print
+   another warning to the console to inform you that the contents of the remote
+   file has changed. If you do not accept the prompt, then Task will exit with
+   code `104` (not trusted) and nothing will run. If you accept the prompt, the
+   checksum will be updated and the remote Taskfile will run.
+
+Task currently supports both `http` and `https` URLs. However, the `http`
+requests will not execute by default unless you run the task with the
+`--insecure` flag. This is to protect you from accidentally running a remote
+Taskfile that is hosted on and unencrypted connection. Sources that are not
+protected by TLS are vulnerable to [man-in-the-middle
+attacks][man-in-the-middle-attacks] and should be avoided unless you know what
+you are doing.
+
+## Caching & Running Offline
+
+If for whatever reason, you don't have access to the internet, but you still
+need to be able to run your tasks, you are able to use the `--download` flag to
+store a cached copy of the remote Taskfile.
+
+<!-- TODO: The following behavior may change -->
+
+If Task detects that you have a local copy of the remote Taskfile, it will use
+your local copy instead of downloading the remote file. You can force Task to
+work offline by using the `--offline` flag. This will prevent Task from making
+any calls to remote sources.
+
+<!-- prettier-ignore-start -->
+[remote-taskfiles-experiment]: https://github.com/go-task/task/issues/1317
+[man-in-the-middle-attacks]: https://en.wikipedia.org/wiki/Man-in-the-middle_attack
+<!-- prettier-ignore-end -->