feat(*) wasm_socket unix domain socket support

[casimiro]

• Update wasm_socket port parsing
• Add test cases (sanity, missing socket file, missing :authority)
• Update tests relying TEST_NGINX_SERVER_PORT2 to use unix domain socket instead.
• If possible, drop TEST_NGINX_SERVER_PORT2

Updating tests that were using TEST_NGINX_SERVER_PORT2 ended up being a substantial amount of work on it's own, deserving it's own PR or PRs.

[coveralls]

Pull Request Test Coverage Report for Build 5835182693

• 15 of 16 (93.75%) changed or added relevant lines in 1 file are covered.
• 4 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.02%) to 91.034%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/common/ngx_wasm_socket_tcp.c	15	16	93.75%

Files with Coverage Reduction	New Missed Lines	%
src/http/proxy_wasm/ngx_http_proxy_wasm_dispatch.c	1	91.81%
src/common/ngx_wasm_socket_tcp.c	3	86.71%

Totals
Change from base Build 5828356494:	0.02%
Covered Lines:	7544
Relevant Lines:	8287

---

💛 - Coveralls

[thibaultcha]

Overall I am weary that our host parsing logic is not integrated within ngx_wasm_sock, which is what I had in mind for this feature... I know the dispatch caller already does some parsing ahead of delegating to ngx_wasm_sock, but moving more parsing logic to ngx_wasm_sock (or validating logic) is also something I would have liked to be explored.

[casimiro]

Thank you for the detailed review @thibaultcha! I'll change the code to address all comments.