Fix tagging of docker images when releasing fleet

[lucasmrod]

💥  Actual behavior

When releasing fleet, the scripts always tag fleetdm/fleet:latest.
This breaks when releasing patches to older minor versions.

E.g.

1. Fleet releases 4.64.0, so fleetdm/fleet:latest is now fleetdm/fleet:v4.64.0.
2. Fleet releases a patch to minor version 63, e.g. 4.63.1, so fleetdm/fleet:latest is now fleetdm/fleet:v4.63.1.

Which means customers/users using fleetdm/fleet:latest experience a downgrade (with e.g. DB migrations issues).

Link to reports from the community:

• https://macadmins.slack.com/archives/C0214NELAE7/p1741286353853189
• https://osquery.slack.com/archives/C01DXJL16D8/p1741282593931279

🕯️ More info (optional)

We should only tag latest if the version that is being released is the highest.

Seems the issue is here:

fleet/.goreleaser.yml

Line 122 in 6886365

- 'fleetdm/fleet:latest'

Possible solution:

• Remove fleetdm/fleet:latest from .goreleaser.yml
• Add some condition to the script to do the tagging of fleetdm/fleet:latest only when the version being released is the highest. (We need this manual step to be executed as the fleetreleaser user in Docker hub to not have the email of the person releasing as the "author" of the tagging).

[lucasmrod]

@lukeheath @georgekarrv