Updater DLL replacement & documentation

[Starkku]

This PR replaces the updater DLL with a modified one based on the original. Source code for the new DLL and the second-stage updater for now are available in a private repository under CnCNet organization.

Includes a documentation for updater and its features, as well as the version file writer that has now been included along with the updater scripts and the second-stage updater executable in the client repository.

Migration information:

• Updater no longer has hardcoded list of download mirrors or custom components. This information must now be set in UpdaterConfig.ini (example is included amongst default resources in client repository). For a reference, the previously hardcoded information can be found in format used by UpdaterConfig.ini here.
• Second-stage updater no longer has hardcoded list of launcher executables to check for when restarting the client. It will now only check ClientDefinitions.ini for LauncherExe key, and it it fails to read and launch this the client will not automatically restart after updating.
• Updater DLL filename has been changed from DTAUpdater.dll to ClientUpdater.dll and second-stage updater from clientupdt.dat to SecondStageUpdater.exe and has been moved from base folder to Resources.

[github-actions[bot]]

Nightly build for this pull request:

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[Starkku]

Fixed the issues pointed out.