main.html: add meta

Описание

Add the following to every page:

    <meta name="GIT_DESCRIBE" content="1a949df">
    <meta name="PICODATA_DOC_VER" content="asabirov_add_meta_tags">

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• Close #206 (closed)
• Target branch: main
• Changes should be cherry-picked to 24.2: no
• Staging: https://docs.binary.picodata.io/picodata/asabirov_add_meta_tags/