DOC: internals: update the SSL architecture schema

Add the new relation between the CA file tree entries and the ckch
instances introduced during CA file hot update implementation (see
GitHub #1057).
diff --git a/doc/internals/ssl_cert.dia b/doc/internals/ssl_cert.dia
index 422d306..52496a1 100644
--- a/doc/internals/ssl_cert.dia
+++ b/doc/internals/ssl_cert.dia
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