chore: migrate to ursa-proxy

[kckeiks]

Description

• feat(proxy): proxy can add headers to responses #333
• feat(proxy): add let's encrypt compatibility #330
• feat(proxy): add cache #345
• feat(proxy): safe shutdown #359
• feat(proxy): file size limit #375 (client_max_body_size)

I don't think we need to do these below before testnet but ping me and we can discuss.

• proxy_cache_path
• Configure HTTP method responses (proxy_cache_methods).
• Configure how long to store the response (so 10mins for 200 and 1s for 404, for example) (proxy_cache_valid)
• Allow users to configure the cache key (proxy_cache_key).
• Defining a shared memory zone used for caching (proxy_cache)
• client_body_buffer_size
• proxy_connect_timeout
• proxy_send_timeout
• proxy_read_timeout
• proxy_buffers