MEDIUM: ssl: set FIPS-approved curve defaults for AWS-LC FIPS builds

MEDIUM: ssl: set FIPS-approved curve defaults for AWS-LC FIPS builds

When AWS-LC is built in FIPS mode, unconditionally override the
compile-time curve defaults with the FIPS-approved NIST P-curves
before config parsing. Explicit ssl-default-{bind,server}-curves
keywords in the global section still take precedence over these
defaults.

The approved set is defined as macros in include/haproxy/defaults.h
alongside the existing CONNECT/LISTEN_DEFAULT_FIPS_CIPHERS family:
  CONNECT/LISTEN_DEFAULT_FIPS_CURVES - P-256, P-384, P-521

This ensures that internal servers (httpclient, Lua SSL sockets) that
inherit global defaults also operate with FIPS-compliant curve lists
without requiring explicit configuration.