ESP8266 and ESP32 build image updates

ESP32: 2.0-r6
ESP8266: 2.0.0-1.5.0-r5

This brings updated mbedTLS with support for on-disk CA chains:
https://github.com/cesanta/mbedtls/compare/esp32_2.0-r5...esp32_2.0-r6
ESP8266 gets bigger rollup (ESP32 got those changes earlier, seems ok):
https://github.com/cesanta/mbedtls/compare/esp8266...esp8266_2.0.0-1.5.0-r5

Saves ~1.5K RAM for now, but will allow adding more roots to ca.pem without wasting RAM.

Refactored docker build for ESP8266 in the same way as was done earlier for ESP32.

PUBLISHED_FROM=db8eb0f91875d02266a8baaf1141c0d65eb59674

mongoose.c

@@ -4602,6 +4602,12 @@ static void mg_ssl_if_mbed_free_certs_and_keys(struct mg_ssl_if_ctx *ctx) {
   }
   if (ctx->ca_cert != NULL) {
     mbedtls_ssl_conf_ca_chain(ctx->conf, NULL, NULL);
+#ifdef MBEDTLS_X509_CA_CHAIN_ON_DISK
+    if (ctx->ca_cert->ca_chain_file != NULL) {
+      MG_FREE((void *) ctx->ca_cert->ca_chain_file);
+      ctx->ca_cert->ca_chain_file = NULL;
+    }
+#endif
     mbedtls_x509_crt_free(ctx->ca_cert);
     MG_FREE(ctx->ca_cert);
     ctx->ca_cert = NULL;
@@ -4687,9 +4693,16 @@ static enum mg_ssl_if_result mg_use_ca_cert(struct mg_ssl_if_ctx *ctx,
   }
   ctx->ca_cert = (mbedtls_x509_crt *) MG_CALLOC(1, sizeof(*ctx->ca_cert));
   mbedtls_x509_crt_init(ctx->ca_cert);
+#ifdef MBEDTLS_X509_CA_CHAIN_ON_DISK
+  ca_cert = strdup(ca_cert);
+  if (mbedtls_x509_crt_set_ca_chain_file(ctx->ca_cert, ca_cert) != 0) {
+    return MG_SSL_ERROR;
+  }
+#else
   if (mbedtls_x509_crt_parse_file(ctx->ca_cert, ca_cert) != 0) {
     return MG_SSL_ERROR;
   }
+#endif
   mbedtls_ssl_conf_ca_chain(ctx->conf, ctx->ca_cert, NULL);
   mbedtls_ssl_conf_authmode(ctx->conf, MBEDTLS_SSL_VERIFY_REQUIRED);
   return MG_SSL_OK;