Use readline and add tethering

[EddyTheCo]

Use readline to add completion, line editing, and interactive history manipulation to the connmanctl_dbus example app.
Fix some small issues in the example and in the property value mapping of the services.
Remove the use of the standard output streams when getting properties. The consumer should define the output stream to put the properties.
Add methods to set the tethering properties of the technologies.
Add tethering tests.

[gemini-code-assist]

Code Review

This pull request integrates the readline library into the connmanctl example to provide command history and auto-completion, while also adding comprehensive support for tethering management along with corresponding test cases. Additionally, it refactors the property logging system to use standard stream operators and removes redundant header includes. Reviewers noted a misspelling in the IPv6 privacy configuration, potential runtime exceptions from std::stoi usage, limitations in the auto-completion logic for multi-argument commands, and a redundant thread notification call.

[github-actions]

🧩 Build Artifacts

✅ The following build artifacts were produced:

• GitHub Actions 1000000639

[github-actions]

🧩 Build Artifacts

✅ The following build artifacts were produced:

• GitHub Actions 1000000643