feat: set the program environment variables

[aymanbagabas]

This adds the option to provide a custom set of environment variables to use in the Bubble Tea program. When running Bubble Tea in a remote session such as SSH, we need to be able to pass the SSH session's environment variables rather than the server ones.

	// Add the TERM from the SSH session to the environment
	var sess ssh.Session // from the github.com/charmbracelet/ssh package
	pty, _, _ := sess.Pty()
	environ := append(sess.Environ(), "TERM="+pty.Term)
	p := tea.NewProgram(model{}, tea.WithEnvironmen(environ))

Now, the Bubble Tea program running for a remote session can determine the appropriate color profile from the session's environment variables instead of the server's environment variables.

In most cases you'll only need this feature when using Bubble Tea in remote sessions.

[meowgorithm]

This is awesome

[caarlos0]

amazing!

[meowgorithm]

Two questions with this one:

• Will it have any effect on local programs?
• How would the user implement it in Wish?

I'd also add a very short example to this PR (and probably the doc comments) so we can reference it later.

[aymanbagabas]

Added an example in the code comment

• Will it have any effect on local programs?

No, bubbletea programs default to os.Environ() if no environment is set.

• How would the user implement it in Wish?

The bubbletea middleware should pass the SSH session's environment to the program. The middleware should include something like:

	var sess ssh.Session // ssh.Session is a type from the github.com/charmbracelet/ssh package
	pty, _, _ := sess.Pty()
	environ := append(sess.Environ(), "TERM="+pty.Term)
	p := tea.NewProgram(model, tea.WithEnvironment(environ)