cli/command/container: deprecate NewDiffFormat, DiffFormatWrite

[thaJeztah]

cli/command/container: deprecate NewDiffFormat

It's part of the presentation logic of the cli, and only used internally.
We can consider providing utilities for these, but better as part of
separate packages.

cli/command/container: DiffFormatWrite: remove intermediate var

Also rename "ctx" argument; we shouldn't use this as name for things
that are not a context.Context.

cli/command/container: newDiffContext: use struct-literal

cli/command/container: deprecate DiffFormatWrite

It's part of the presentation logic of the cli, and only used internally.
We can consider providing utilities for these, but better as part of
separate packages.

- Human readable description for the release notes

Go SDK: cli/command/container: deprecate `NewDiffFormat`, `DiffFormatWrite`. These functions were only used internally and will be removed in the next release.

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

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 80.00000% with 3 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
cli/command/container/formatter_diff.go	76.92%	3 Missing ⚠️

📢 Thoughts on this report? Let us know!

[thaJeztah]

Flaky test;

65.93 === Failed
65.93 === FAIL: cli/command/system TestSystemPrunePromptTermination (0.00s)
65.93     prune_test.go:80: assertion failed: error is "system prune has been cancelled" (system.cancelledErr), not "prompt terminated" (prompt.ErrTerminated prompt.cancelledErr)