Setup mailman3 server

We want to migrate to mailman3 as mailman2 is basically unmaintained and requires Python 2 which is EOL.

Because the mailman and mailman3 packages conflict and we don't want to perform a big bang migration, mailman3 must be deployed on a separate server. mailman-web (mailman3's web interface) hasn't been packaged yet, so for now we are using my homebrewed PKGBUILD.

[1] https://gist.github.com/klausenbusk/5982063f95c503754a51ed2fefb8915e

Ref #59 (closed)

---

Migrated lists:

• arch-announce
• arch-devops-private
• arch-events
• arch-wiki-admins

group_vars/all/vault_mailman3.yml

+$ANSIBLE_VAULT;1.1;AES256
+34383835323639306337626539636433613539636466653630383234333063623930666137646438
+6631373661313934656531363265363061313132633031650a326434306636396139663436623133
+38303738636465343430396461353533336165353033356430613036623136353137316338363364
+6563386438653733610a636566326462346364323362666639373430626663353935393763343638
+34393436616131376639653238326266336161393130386232373836303831646133303133313639
+65666136303433636632663261363930626161623938353033623761663264643831353063616432
+61373963636164663832666532313833656133363434323831323364643561616134616536646538
+30363632366661333936663139666166303737316166383738653038343034396265313466643532
+64646532393239613631653336633361346664343561643734316336363632383935653534323263
+38616463366235366636633839663464393562316138343534666430643266663439363838353239
+65643030666564343661343466646333313566333561646662623731656666353166626566333637
+31656432613439366661343834636239356139663263303965653430336662396431643966303739
+37316166663132363062323533646131623630666332653565303630613039666231323130386139
+34393639366537343463393133643832653133333065363839663333366333626132306636663136
+36316464623664303762316461386235643363353262323535383065346563613261623966313530
+37303466623834333537346265323766633934366332396436643962306637643262343463383963
+39393332633465333864346437383533633465343632323061623833393739646361383766656131
+31393066633364646637333765303266363438373330326334323666653262396137363036373734
+38663339326435383730366532363264386334376533653030343430633836376261346237646638
+37663864633832623237623335313938616562356366303638386531323035613534323130333439
+31613931636238373864303166623636643735383837343464323663633263313963626632633031
+64626535333231623461656661323264636333613430366637333631306663343438353763393537
+37663034336338376538333632623939643165613836656334323638653133333362393632653131
+38663937633065313531376134333238346163636162386665306332363635653934363761396339
+3366