Add action to enter wifi AP mode (or update documentation)

**Describe the problem you have/What new integration you would like**
The [documentation for the wifi component](https://esphome.io/components/wifi.html) refers to enabling AP mode by a button press, as an alternative way to enable it when `ap_timeout` is set to 0 secs.

However, there does not appear to be any action which can be configured to trigger the wifi component to enter AP mode, nor an example in the documentation of doing so (i.e. configuring a button press sequence to enable AP mode).

**Please describe your use case for this integration and alternatives you've tried:**
When using manually configured APs or IP addresses, it can be difficult to setup a component for reflashing OTA (particularly with components without easy serial access without disassembly) if the original network is still in use or the configured SSID is still available. This would be particularly useful when manually assigned IP addresses are being used, and a device is in conflict or has been replaced and is for whatever reason not easily accessible.

I would like to be able to configure my devices so a button press, or multi-press sequence would trigger the device to disconnect / cease attempting to connect to any existing wifi configuration it has, and instead immediately start AP mode instead (with any AP mode configuration it has) even if a configured SSID is broadcasting.

Additionally it would be nice to be able to combine this with safe mode, so "safe mode with AP mode" was an option - rather then the device simply rebooting but keeping it's wifi configuration.

**Additional context**