migrations: Adds new migration for bumping host container versions

[etungsten]

Adds migration for the default admin and control container versions v0.1 <-> v0.2

Issue #, if available: #534

Description of changes:

Testing done:
Locally testing forward migration, and it bumps version correctly from v0.1 to v0.2:

$ echo '"328549459982.dkr.ecr.us-west-2.amazonaws.com/thar-admin:v0.1"' > ds/live/settings/host-containers/admin/source
$ cargo run -- --datastore-path ds --forward
    SNIP
     Running `/home/ANT.AMAZON.COM/etung/thar/PRIVATE-thar/workspaces/target/debug/host-containers-version-migration --datastore-path ds --forward`
$ cat ds/live/settings/host-containers/admin/source 
"328549459982.dkr.ecr.us-west-2.amazonaws.com/thar-admin:v0.2"

Run again:

$ cargo run -- --datastore-path ds --forward
$ cat ds/live/settings/host-containers/admin/source 
"328549459982.dkr.ecr.us-west-2.amazonaws.com/thar-admin:v0.2"

If the admin container is a custom container, no modification is made:

$ echo '"super-cool-custom-admin-containerv123"' > ds/live/settings/host-containers/admin/source
$ cargo run -- --datastore-path ds --forward
$ cat ds/live/settings/host-containers/admin/source 
"super-cool-custom-admin-containerv123"

For control container, same, bumps version correctly from v0.1 to v0.2:

$ echo '"328549459982.dkr.ecr.us-west-2.amazonaws.com/thar-control:v0.1"' > ds/live/settings/host-containers/control/source
$ cargo run -- --datastore-path ds --forward
$ cat ds/live/settings/host-containers/control/source 
"328549459982.dkr.ecr.us-west-2.amazonaws.com/thar-control:v0.2"

For backwards migration, admin downgrades from v0.2 to v0.1:

$ cat ds/live/settings/host-containers/admin/source 
"328549459982.dkr.ecr.us-west-2.amazonaws.com/thar-admin:v0.2"
$ cargo run -- --datastore-path ds --backward
$ cat ds/live/settings/host-containers/admin/source 
"328549459982.dkr.ecr.us-west-2.amazonaws.com/thar-admin:v0.1"

Backwards control container version migration:

$ cat ds/live/settings/host-containers/control/source 
"328549459982.dkr.ecr.us-west-2.amazonaws.com/thar-control:v0.2"
$ cargo run -- --datastore-path ds --backward
$ cat ds/live/settings/host-containers/control/source 
"328549459982.dkr.ecr.us-west-2.amazonaws.com/thar-control:v0.1"

Tested in live Thar instance, launched Thar v0.1.6 (datastore version v0.0), loaded new image into side B using dd, loaded migrations, ran updates and verified that default image versions got bumped:

bash-5.0# signpost status                                                                                                                   min/source
OS disk: /dev/nvme0n1
Set A:   boot=/dev/nvme0n1p2 root=/dev/nvme0n1p3 hash=/dev/nvme0n1p4 priority=1 tries_left=0 successful=true
Set B:   boot=/dev/nvme0n1p6 root=/dev/nvme0n1p7 hash=/dev/nvme0n1p8 priority=2 tries_left=0 successful=true
Active:  Set B
Next:    Set B
bash-5.0# cat /var/lib/thar/datastore/current/live/settings/host-containers/admin/source                                                    
"328549459982.dkr.ecr.us-west-2.amazonaws.com/thar-admin:v0.2"

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[sam-aws]

This migration should be under migrations/v0.2 right?

[etungsten]

Addresses @tjkirch 's comments:
Use constants for the image names
Other clean ups.

Tests still pass.

[sam-aws]

Ah wait, we're going from 0.0 -> 0.1, all good ;)

[etungsten]

Addresses @tjkirch 's comments on constant use

[zmrow]

🏙