global: Add reasons to mailbox_transaction_begins

src/lib-sieve-tool/mail-raw.c

src/lib-sieve/sieve-actions.c

src/lib-sieve/sieve-message.c

src/lib-sieve/sieve-storage-sync.c

src/lib-sieve/util/edit-mail.c

src/plugins/imapsieve/imap-sieve-storage.c

src/sieve-tools/sieve-filter.c

src/testsuite/testsuite-mailstore.c