Add ESP-IDF support

[urwrstkn8mare]

This pull request adds support for integrating the lwgps library as a component in ESP-IDF projects. The changes introduce conditional CMake logic for ESP-IDF and updates README.md with integration instructions.

ESP-IDF integration:

• Added conditional logic in CMakeLists.txt to detect ESP-IDF builds, configure the options header (lwgps_opts.h), and register lwgps as an ESP-IDF component. This allows users to customize configuration and seamlessly include the library in their ESP-IDF projects.
• Added idf_component.yml with a dependency on ESP-IDF version 5.0 or higher, ensuring compatibility with modern ESP-IDF toolchains.

Documentation updates:

• Updated README.md with detailed instructions for integrating lwgps as an ESP-IDF component, including configuration options and example CMake usage.

[tuupola]

ESP_PLATFORM can be used to check that this is an ESP-IDF build.

IDF_PATH tells the path to the ESP-IDF directory but not necessarily that this is an ESP-IDF build.

[urwrstkn8mare]

Thanks @tuupola and @MaJerle for the feedback. I've addressed them so if you'd like to re-review. Hopefully putting the ESP-IDF in the get-started page is fine it seemed to make the most sense.