feat: self update

[ghost]

Description

Adds the dfxvm self update command.

Fixes https://dfinity.atlassian.net/browse/SDK-1272

How Has This Been Tested?

Added tests

Tested locally by:

• change Cargo.toml version and rebuild
• run dfxvm self update
• it downloads and extracts the tarball, but fails when trying to call the contained binary with dfxvm-init --self-replace, since the older releases obviously don't support this functionality
• copied the dfxvm binary over the dfxvm-init-self-update binary in the bin directory
• called dfxvm-init-self-update --self-replace in the bin directory

Checklist:

• I have edited the CHANGELOG accordingly.
• I have made corresponding changes to the documentation in docs/cli-reference.

[viviveevee]

Suggested change

	#[error("failed to execute {command:#?}")]
	#[error("failed to execute {command:#?}. Error: {source}")]

I feel like having the error available would make support on e.g. the forum much easier

[ghost]

This happens automatically, because the variable is called source. See https://github.com/dfinity/dfxvm/blob/main/src/log.rs#L30