lib: TLS session ticket caching reworked

Described in detail in internal doc TLS-SESSIONS.md

Main points:
- use a new `ssl_peer_key` for cache lookups by connection filters
- recognize differences between TLSv1.3 and other tickets
  * TLSv1.3 tickets are single-use, cache can hold several of them for a peer
  * TLSv1.2 are reused, keep only a single one per peer
- differentiate between ticket BLOB to store (that could be persisted) and object instances
- use put/take/return pattern for cache access
- remember TLS version, ALPN protocol, time received and lifetime of ticket
- auto-expire tickets after their lifetime

Closes #15774

lib/Makefile.inc

@@ -56,6 +56,7 @@ LIB_VTLS_CFILES =           \
   vtls/schannel_verify.c    \
   vtls/sectransp.c          \
   vtls/vtls.c               \
+  vtls/vtls_scache.c        \
   vtls/wolfssl.c            \
   vtls/x509asn1.c
 
@@ -74,6 +75,7 @@ LIB_VTLS_HFILES =           \
   vtls/sectransp.h          \
   vtls/vtls.h               \
   vtls/vtls_int.h           \
+  vtls/vtls_scache.h        \
   vtls/wolfssl.h            \
   vtls/x509asn1.h