Update User-Agent Version for Crawler

[marevol]

This issue addresses the need to update the user-agent version used by the crawler. The current version of the user-agent is outdated and requires an update to reflect the latest version.

Changes:

• The user-agent prefix and suffix constants (CRAWLING_USER_AGENT_PREFIX and CRAWLING_USER_AGENT_SUFFIX) are added in Constants.java.
• In WebConfig.java, the logic is updated to use these new constants when setting the user-agent.
• In FessProp.java, the method getUserAgentName() is modified to utilize the new constants along with the product version.

These changes ensure that the crawler's user-agent is always up-to-date with the current version of the Fess, improving compatibility and identification during web crawling.