SFU add download function and OTA example

[pennam]

Should fix #152 Needs #134

[yann-l]

Hi,
First thanks for this work, such a function is really missing. in IoT, we do need to be able to update the firmware, and of course not from a .h file.

2 comments though:

• in HTTP: I'm not able to download an ota file. If I try your ota file(330ko) it stops downloading at about 250-300ko, if I try my own ota file (450ko) it stops at about 350ko).

• It doesn't work over HTTPS:

22:11:18.681 -> ssl_msg.c:1419: mbedtls_cipher_auth_decrypt_ext() returned -25344 (-0x6300)
22:11:18.681 -> ssl_msg.c:3763: ssl_decrypt_buf() returned -29056 (-0x7180)
22:11:18.681 -> ssl_msg.c:3918: ssl_get_next_record() returned -29056 (-0x7180)
22:11:18.681 -> ssl_msg.c:5501: mbedtls_ssl_read_record() returned -29056 (-0x7180)
22:11:18.681 -> [data_to_read():400]: (-29056) SSL - Verification of the message MAC failed

downloading big files (more than 2-3ko) doesn't work with WiFiSSLClient. Here is the exact problem I have and an (IMHO) ugly but working workaround: https://stackoverflow.com/questions/75941895/why-does-my-https-request-get-disconnected-on-large-files
using HTTPS is mandatory for obvious security reasons, and ota files are too big.

EDIT: After applying #134 it works with HTTP and HTTPS. Great work!

[pennam]

@yann-l yes, this PR needs #134 to work properly with WiFi. I've updated the description.

Thanks for testing!

[facchinm]

The CI error is expected since the download() API is not art of 1.0.4 core. Merging.