ci(Taskfile): add a command to test autoupdate

[dido18]

Please check if the PR fulfills these requirements

• The PR has no duplicates (please search among the Pull Requests
  before creating one)
• Tests for the changes have been added (for bug fixes / features)

What kind of change does this PR introduce?
Feature for local testing of autoupdate.

What is the current behavior?

What is the new behavior?
Add an autoupdate:demo command to test the autoupdate of the agent on local machine.

• By default, the new version is the current commit.
• To provide a custom version, pass the VERSION=X.Y.Z to the task command.

Usage:

╰─$ task autoupdate:demo VERSION=3.0.3
Before continuing, please make sure you’ve opened the "Open Configuration" option from the Agent menu and set the updateUrl=http://127.0.0.1:3000/ [y/N]
y
task: [go:build] go build -v  -o arduino-cloud-agent -ldflags ' -X main.version=3.0.3 -X main.commit=b8c7f9e '
github.com/arduino/arduino-create-agent
task: [autoupdate:demo] go install github.com/sanbornm/go-selfupdate/...@latest
task: [autoupdate:demo] go-selfupdate -o public/CreateAgent/Stable ./arduino-cloud-agent 3.0.3
task: [autoupdate:demo] docker rm -f agent-static-server
agent-static-server
task: [autoupdate:demo] docker run --rm -d -v "$PWD/public:/usr/share/nginx/html:ro" -p 3000:80 --name agent-static-server nginx:alpine
ef6dfeaa9bd2b0b031c558c2f3cf4c214b9b77428bf74ad23371fb67ab92aedd
task: [autoupdate:demo] sleep 5
task: [autoupdate:demo] curl -X POST http://127.0.0.1:8991/update
{"success":"Please wait a moment while the agent reboots itself"}%   

To check that the update process was completed correctly, click on the tray icon of the agent and check the Agent Version X.X.X

• Does this PR introduce a breaking change?

• Other information:

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 20.24%. Comparing base (e7ea376) to head (e2d2c38).

Additional details and impacted files

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  Coverage   20.24%   20.24%           
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  Files          42       42           
  Lines        3241     3241           
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  Hits          656      656           
  Misses       2498     2498           
  Partials       87       87           

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[alessio-perugini]

Just add a note that when chaning the config, we have to restart the agent otherwise the very firstrun of this task won't work, as the old agent picked up the default url