php-gd extension is required for Drive setImage

[phil-davis]

$ make test-php-phan
composer install
Installing dependencies from lock file (including require-dev)
Verifying lock file contents can be installed on current platform.
Nothing to install, update or remove
Generating autoload files
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vendor/bin/phan --config-file .phan/config.php --require-config-exists
   analyze ████████████████████████████████████████████████████████████ 100.0% 950MB/960MB
src/Drive.php:340 PhanUndeclaredTypeParameter Parameter $image has undeclared type \GdImage
make: *** [Makefile:61: test-php-phan] Error 1

After I do sudo apt install php-gd then it passes.

But this is currently only needed by:

    /**
     * @todo This function is not implemented yet! Place, name and signature of the function might change!
     */
    public function setImage(\GdImage $image): Drive
    {
        // upload image to dav/spaces/<space-id>/.space/<image-name>
        // PATCH space
        throw new NotImplementedException(Ocis::FUNCTION_NOT_IMPLEMENTED_YET_ERROR_MESSAGE);
    }

which is not implemented yet anyway.

And README only has:

### Required PHP Libraries
- php-bcmath
- php-gmp

Should we remove \GdImage from the parameter declaration for now? (and write a comment that \GdImage is expected to be the parameter type when implemented)

That will avoid this silly little thing in the current v1 releases.

[individual-it]

yes, please do that