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

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

When AWS-LC is built in FIPS mode, unconditionally override the
compile-time signature algorithm defaults with the FIPS-approved set
before config parsing. Explicit ssl-default-{bind,server}-sigalgs
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_SIGALGS        - ECDSA (P-256/384/521),
                                               RSA-PSS and RSA-PKCS1
                                               with SHA-256/384/512
  CONNECT/LISTEN_DEFAULT_FIPS_CLIENT_SIGALGS - same set for client
                                               certificate sigalgs

SHA-1 based algorithms and non-FIPS primitives (ed25519, ed448) are
excluded from the defaults.