Support --json output for status command

[AliSoftware]

What

Allows to easily use the output in scripts if needed (e.g. pipe that status output through jq, etc)

How

• Introduce dedicated struct RepositoryStatus object to represent the status reported by git-conceal status
• Introduce dedicated struct FileStatusList and struct FileStatus objects to represent the status of files list reported by git-conceal status file1 file2 …
• Make those structs implement both the Serialize trait from the serde crate—to handle JSON serialization (using #[derive(Serialize)] for implicit implementation of it)—and the fmt::Display trait—to handle plain text rendering.
• Which allows the implementation of cmd_status to build those objects representations regardless of the output format requested, and only at the end decide to println! those results either as JSON (serde_json::to_string_pretty(&status)) or as plain text (print!("{}", status)). (Making the code nicer than if I did giant if / else branches for all the cases)

Testing Instructions

• Run cargo build --release from this PR's head branch
• Checkout the head branch of one of the PRs of a repo in which I've already prepared the migration to git-conceal, like of [AINFRA-1533] Adopt git-conceal in this repo woocommerce/woocommerce-android#14979 or [AINFRA-1539] [Internal] Migrate from configure_apply to git-conceal pocket-casts-android#4841, so you have a repo on which to test that command on
• Then, from the working copy of such a test repo, run some commands to test the feature, like:

$ export PATH="<path-to-git-conceal-repo>/target/release:$PATH"
$ git-conceal status --json | jq
$ git conceal status --json | jq -r '.encrypted_files[]'
$ git conceal status --json secret.properties | jq
$ git conceal status --json secret.properties foo bar baz | jq '.files | map({key:.file, value:.encrypted}) | from_entries'

[iangmaia]

Maybe this can be an enum? Something like:

#[derive(Serialize)]
#[serde(rename_all = "lowercase")] // see https://serde.rs/container-attrs.html#rename_all
pub enum LockStatus {
    Locked,
    Unlocked,
}

[AliSoftware]

Good idea, I like it 👍

[AliSoftware]

Implemented in 1427abf

[iangmaia]

Code looks good 👍 and I ran the test instructions in PCAndroid and it's working as expected