add latest docu of blockly features of M2

[stefan-hoehn]

This adds missing documentation for the following new blockly features

• https://github.com/openhab/openhab-webui/pull/2175 Add parse number block
• https://github.com/openhab/openhab-webui/pull/2174 persistence previous state value as number
• https://github.com/openhab/openhab-webui/pull/2411 HTTP request block
• https://github.com/openhab/openhab-webui/pull/2465 Add undefined block
• https://github.com/openhab/openhab-webui/pull/2562 New Thing blocks
• https://github.com/openhab/openhab-webui/pull/2564 breaking change persistence
• https://github.com/openhab/openhab-webui/pull/2575 add timer context

and many more small corrections

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[openhab-bot]

This pull request has been mentioned on openHAB Community. There might be relevant details there:

https://community.openhab.org/t/openhab-4-2-milestone-discussion/154316/129