Rename receiver_msp/index.html by receiver_msp/receiver_msp.html

[McGiverGim]

Follow up of https://github.com/betaflight/betaflight-configurator/pull/3939

In my first tests, for some reason it didn't work if I let it as receiver_msp.html so I renamed it to index.html. Now it seems to be working, so I rename it again to make it clearer.

I can make it working if I move to a subfolder inside tabs, so I've left it in the src/receiver_msp and moved the css and js to similar folders for coherence.

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[sonarqubecloud[bot]]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
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