Add ecosystem section to apisix website

This will allow contributors to submit and document APISIX-related tools they have developed, allowing them to gain attention.

For example, the [ADC](https://github.com/api7/adc) for supporting GitOps could be listed as an eco-project.

Start by reviewing the APISIX website structure and its contributor documentation to determine where an ecosystem section and submission flow would belong. Use the ADC example to define the information each project should provide; done means contributors can submit APISIX-related tools and visitors can discover and understand them.

Written by the indexing model from the issue text.