Patch workshop xauth cookie with wildcard entry during migrate

[lachypjones]

Description

Currently x11 apps using the desktop interface will fail on several official flavors such as Xubuntu (all versions) and Kubuntu 20.04. This PR introduces a minimal xauth parser, used to patch the Xauthority cookie with a wildcard prior to migrating it into the daemon runtime directory.

Known Issues

A logout followed by an immediate login will cause workshop to fail to update the Xauthority cookie. This is not a regression

Self-review quick check

• Make decisions that cost a lot to reverse explicit in the PR description.
• Avoid nested conditions.
• Delete dead code and redundant comments.
• Normalise symmetries by sticking to doing identical things identically.

// one way to handle errors
if err := f(); err != nil {
   ...
}

// one way to handle multiple returns
val, err := f()
if err != nil {
   ...
}
...

• Check that coupled code elements, files, and directories are adjacent. For example, test data is stored as close as possible to a test.
• Put variable declaration and initialisation together.
• Divide large expressions into digestable and self-explanatory ones. Use multiple variables if required.
• Put a blank line between two logically different chunks of code.
• Follow the style guide for new error messages.

Docs

• I have checked and added or updated relevant documentation.
• I have checked and added or updated relevant release notes.
• I have included the technical author in the review.

Or:

• I confirm the PR has no implications for documentation.