feat(prefix): update the list of yieldable phases

[HanadaLee]

add precontent, proxy_ssl_cert and proxy_ssl_verify phases. They are newly introduced phases.
rename ssl_certificate to ssl_cert, because the api ngx.get_phase use ssl_cert instead of ssl_certificate.

see also
https://github.com/openresty/lua-resty-core/blob/master/lib/resty/core/phase.lua

local context_names = {
    [0x00000001] = "set",
    [0x00000002] = "rewrite",
    [0x00000004] = "access",
    [0x00000008] = "content",
    [0x00000010] = "log",
    [0x00000020] = "header_filter",
    [0x00000040] = "body_filter",
    [0x00000080] = "timer",
    [0x00000100] = "init_worker",
    [0x00000200] = "balancer",
    [0x00000400] = "ssl_cert",
    [0x00000800] = "ssl_session_store",
    [0x00001000] = "ssl_session_fetch",
    [0x00002000] = "exit_worker",
    [0x00004000] = "ssl_client_hello",
    [0x00008000] = "server_rewrite",
    [0x00010000] = "proxy_ssl_verify",
    [0x00020000] = "precontent",
    [0x00040000] = "proxy_ssl_cert",
}

https://github.com/openresty/lua-nginx-module/blob/master/src/ngx_http_lua_util.h

#define NGX_HTTP_LUA_CONTEXT_YIELDABLE (NGX_HTTP_LUA_CONTEXT_REWRITE         \
                                | NGX_HTTP_LUA_CONTEXT_SERVER_REWRITE        \
                                | NGX_HTTP_LUA_CONTEXT_ACCESS                \
                                | NGX_HTTP_LUA_CONTEXT_PRECONTENT            \
                                | NGX_HTTP_LUA_CONTEXT_CONTENT               \
                                | NGX_HTTP_LUA_CONTEXT_TIMER                 \
                                | NGX_HTTP_LUA_CONTEXT_PROXY_SSL_CERT        \
                                | NGX_HTTP_LUA_CONTEXT_PROXY_SSL_VERIFY      \
                                | NGX_HTTP_LUA_CONTEXT_SSL_CLIENT_HELLO      \
                                | NGX_HTTP_LUA_CONTEXT_SSL_CERT              \
                                | NGX_HTTP_LUA_CONTEXT_SSL_SESS_FETCH)