Enable wifi and captive portal in case no ethernet connection could be established

Nobody has claimed this yet.

**Describe the problem you have/What new integration you would like**
I'm using a ESP32 with integrated ethernet connectivity (LILYGO TTGO T-Internet-POE as esp-wrover-kit). This works fine with the ethernet component of type LAN8720. When trying to enable WIFI and ethernet, ESPhome will show the error "Component ethernet cannot be used together with component wifi.". It might be nice to have the possibility to enable both at the same time for connection redundancy, but I guess this will not work due to too few recources or shared pins. But one of the following options would be still nice:
- First try to establish a connection via ethernet. If this fails, start the wifi and try to connect wirelessly
- Have the ESPs wifi access point with the captive portal starting, in case no ethernet connection or wifi could be established

**Please describe your use case for this integration and alternatives you've tried:**

When working on the sensor while it is not connected via ethernet you now have no way of accessing it which can make flashing complicated. Imagine you want to flash a ESP with ethernet which already has a old or unknown firmware on it. Due to the maybe unknown IP settings of the old firmware, you cannot access it via ethernet but need to flash via USB. When the ESP is build into a sealed housing in a dirty environment (like in my case), you cannot just demount the ESP32 and connect USB to it. But you could connect to its wifi access point, if it would start in case of the missing ethernet connection.

**Additional context**

Start from the ESPHome ethernet component, including LAN8720, and the wifi and captive portal components described in the request. Determine how connection fallback should work and whether both components can coexist; done means an ESP32 can recover access through wifi or its captive portal when ethernet cannot connect, with the chosen behavior covered by tests.

Written by the indexing model from the issue text.