contint: cleanup gallium / use contint1001

gallium.wikimedia.org [208.80.154.135] died and is being replaced by
contint1001.eqiad.wmnet [10.64.0.237].

Varnish misc is NOT covered and is handled in an independent change:
https://gerrit.wikimedia.org/r/#/c/293284/

[hiera]
zuul_merger_host: zuul-merger is not on the new server, solely rely on
scandium.eqiad.wmnet for now.
Update some comments for the sshd MAC/KEX legacy algorithms

[contint::firewall::labs]
(impacts CI and deployment-prep slaves on labs)
Rename ferm rule and update IP

[jenkins]
Change jenkins-mwext-sync_id_rsa.pub comment.

[nodepool]
(impacts labnodepool1001.eqiad.wmnet)
Switch ZeroMq end point
Rename CI system name

[zuul]
Gearman is on the private 10.x IP

[role::ci::slave]
Update ssh public key to allow connections from contint1001

[role::ci::master]
Update git email address for the jenkins user.

Bug: T137265
Change-Id: I0a4722b509cfe76ee7f5badbf63b26d05d0f92b0