Change Blockchair Search provider's HTTP method

When searching with the new built-in provider, Blockchair responds with a 405:

Oops! An Error Occurred
The server returned a "405 Method Not Allowed".

Something is broken. Please let us know what you were doing when this error occurred. We will fix it as soon as possible. Sorry for any inconvenience caused.

We should use GET instead of POST.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information