WeCom doesn't pad base64 aeskey, causing Python strict mode decode failure
on media/image/file messages. Add automatic padding before base64 decode:
aes_key + '=' * ((4 - len(aes_key) % 4) % 4).
Salvages the AES padding fix from @chengoak's PR #17040. The SSRF whitelist
entry for a private COS bucket hostname was dropped as it belongs in user
config, not the built-in trusted-private-IP-hosts list. The debug-level
full-body info log was dropped to avoid logging potentially sensitive
message content at INFO level.
8f4c0bf088