Landing page should offer mirror even for download buttons

[georgik]

Right now the user must click "All available downloads" to see mirrors https://dl.espressif.com/dl/esp-idf/

Change the behaviour so that mirror link is also visible when clicking on Download button.

[georgik]

Solution: https://github.com/espressif/idf-installer/commit/e087c8dce17823180f1762ff054c8ff23ff0f2c6