fix: multi-stage image build

[VanillaSpoon]

Use a multi-stage image build for kas-fleet-manager rather than building the binary on the host

Description

Configured a multi-stage image build rather than building the binary on the host. This reduces broken images from incompatible dependencies.

Issue: https://issues.redhat.com/secure/RapidBoard.jspa?rapidView=8806&view=detail&selectedIssue=MGDSTRM-5007&quickFilter=48314

Checklist (Definition of Done)

• All acceptance criteria specified in JIRA have been completed
• Unit and integration tests added that prove the fix is effective or the feature works (tested against emulated and non-emulated OCM environment)
• Documentation added for the feature
• CI and all relevant tests are passing
• Code Review completed
• Verified independently by reviewer
• Required metrics/dashboards/alerts have been added (or PR created).
• Required Standard Operating Procedure (SOP) is added.
• JIRA has created for changes required on the client side

[machi1990]

Left a suggestion about copying only the binary and nothing else.
Otherwise the image size will be bloated for things that we are not interested with.

[VanillaSpoon]

Thanks @machi1990 I'll change that now

[machi1990]

@VanillaSpoon thanks for the PR.

Code change looks good to me.

What steps (commands) would you advise someone take to quickly verify the change locally?

[machi1990]

I'd like this to have another eye, so I've asked a review from @JameelB.

@JameelB would you have some time to look at the PR? it should be quick to review and verify 🤞 Thanks

[VanillaSpoon]

To test this change locally:

1. Make sure that the kas-fleet-manager binary is not in the project root
2. make image/build to build the docker image.
3. docker run <image> to run the image.

(When docker run is executed, there might be errors due to missing secrets. That's normal.)

[JameelB]

Looks good, thanks for this @VanillaSpoon! just one question there :)

[machi1990]

lgtm

let's wait for @JameelB thumbs up on the question before merging.

Thanks a lot for the great shift on this as well as going the extra step in verifying it. @VanillaSpoon