feat: make token TTL and DoS limits configurable via MicroProfile Config

[bmarwell]

Motivation

Several constants are currently hard-coded:

Constant	Location	Value
TOKEN_TTL_HOURS	AddKeyToVerificationQueueCommandHandler	24 h
MAX_EMAIL_UIDS	same	20
MAX_SUBKEYS	(proposed in #136)	50
Max keytext size	(proposed in #135)	128 KB

These should be read from MicroProfile Config so operators can tune them per deployment without recompiling.

Implementation

Add @ConfigProperty injection in the handler(s):

@Inject
@ConfigProperty(name = "keyserver.verification.token-ttl-hours", defaultValue = "24")
int tokenTtlHours;

Provide default values matching the current hard-coded values so behaviour is unchanged out of the box.

Document the properties in docs/ or a src/main/liberty/config/ README.