Minor restructure for ko compatibility

[aidy]

Move cmd/main.go to cmd/trust-manager/main.go so that ko correctly builds as a trust-manager binary. This brings it into line with other go project structures.

This is a noop as far as the current build mechanism is concerned - it should generate the same thing in the same way, but this restructure facilitates an easier development/test cycle.

[jetstack-bot]

Hi @aidy. Thanks for your PR.

I'm waiting for a cert-manager member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[SgtCoDFish]

/ok-to-test

[SgtCoDFish]

/lgtm
/approve

Even without thinking about ko I prefer this structure. Thanks very much!

[jetstack-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aidy, SgtCoDFish

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