dgit-repos-server emailing in accordance with the design

dgit-repos-server is meant to send two e-mails. Both are to be addressed to all of:

• username associated with signing key (e.g. spwhitton@debian.org / iwj@debian.org)

• tagger (e-mail address from git tag object) (e.g. spwhitton@spwhitton.name / ijackson@chiark) (done in !86 (merged))

• debian-tag2upload@lists.debian.org (done in !86 (merged), assuming appropriate config)

• it completes transmission of the first e-mail before doing anything else (done in !86 (merged))

• the first one has only the URL and tag contents (done in !86 (merged))

• the second one has: target distro, package suite and version; salsa URL; whether the operation succeeded; report / shell traanscript of each processing attempt (done in !86 (merged), except for questions in #32 (closed))

Sponsee gets mail from dak, not from us.