Move htmlLabells configuration out of flowchart to root

[knsv]

The configuration for whether or not to use htmlLabels is currently done with this configuration:

{
     flowchart:{
          htmlLabels: true
     }
}

With the new rendering engine more diagram types will get the option of htmlLabels which is why the option needs to move out of flowchart to the root as per below:

{
     htmlLabels: true
}

The change should be done without breaking backwards compatability. If a site integrator does not move the configuration mermaid should still look in the old location (for the time beeing). The current location is deprecated and in v9 support for it will be removed.

[ghost]

Relates to:

• Mermaid 8.0.0-rc.8 creates SVG files that do not display correctly in Inkscape and Latex mermaid-cli#103
• SVG export does not work properly when the exported SVG is used outside Firefox #2102
• Render diagrams using non-browser-based rendering libraries #2485
• SVG conformance ? #1845
• Flowchart rendered differently depending on whether "htmlLabels" is enabled or not #1572
• htmlLabels suport And CSS single Control #1395
• Label texts in flowcharts are not centered horizontally with "htmlLabels" disabled #1177
• Replace foreignObject with standard SVG #2688

[jgreywolf]

Assigning myself for follow up