private @NotNull String getExtensionDirectoryName(final @NotNull File extensionDirectory) throws IOException {
        final File file = new File(extensionDirectory, "hivemq-extension.xml");
        final String xml = FileUtils.readFileToString(file, StandardCharsets.UTF_8);
        final Matcher matcher = EXTENSION_ID_PATTERN.matcher(xml);

        if (!matcher.find()) {
            throw new IllegalStateException("Could not parse extension id from '" + file.getAbsolutePath() + "'");
        }
        return matcher.group(1);
    }
Puts the given extension folder into '/opt/hivemq/temp-extensions/{directory-name}' inside the container.
It must at least contain a valid hivemq-extension.xml and a valid extension.jar in order to be executed.
The directory-name is taken from the id defined in the hivemq-extension.xml.
<p>
Must be called before the container is started.
<p>
The contents of the '/opt/hivemq/temp-extensions/' directory are copied to '/opt/hivemq/extensions/' before the container is started.

@param mountableExtension the extension folder on the host machine
@return self
modules/hivemq/src/main/java/org/testcontainers/hivemq/HiveMQContainer.java