[24.0 backport] api/inspect: Fix nil RepoTags and RepoDigests

[vvoland]

• Backport: api/inspect: Fix nil RepoTags and RepoDigests #45563

#43883 removed the variable initialization to empty arrays which silently changed the API and made it return nil RepoTags and RepoDigests instead of empty arrays.

acd0aa7#diff-2d8d96f6fa256de94f3737c8631e99d897efb15ec869f465f8cfcb8962e70be0R208-R210

(cherry picked from commit 1be26e9)

- What I did
Make RepoTags and RepoDigests empty arrays instead of nil.

- How I did it
Set RepoTags/RepoDigests to empty array if it's nil.

- How to verify it

# Before
$  docker inspect ead3e795a244 | head -n5
[
    {
        "Id": "sha256:ead3e795a244cfa86bff5eda3d7ce08a910b976453132b63a503546c80bfee13",
        "RepoTags": null,
        "RepoDigests": null,

# After
$  docker inspect ead3e795a244 | head -n5
[
    {
        "Id": "sha256:ead3e795a244cfa86bff5eda3d7ce08a910b976453132b63a503546c80bfee13",
        "RepoTags": [],
        "RepoDigests": [],

- Description for the changelog

- A picture of a cute animal (not mandatory but encouraged)

[thaJeztah]

LGTM