feat: Support info metrics (#24)

# What ❔

Adds support of [the info metric
type](https://github.com/OpenObservability/OpenMetrics/blob/main/specification/OpenMetrics.md#info)
and adjacent helpers (e.g., units for labels and `DurationAsSecs`
wrapper).

## Why ❔

Info metrics is the idiomatic way to expose information not changed
during the program runtime (version / git commit, component configs
etc.).

.github/workflows/cargo-license.yaml

@@ -4,5 +4,5 @@ jobs:
   cargo-deny:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - uses: EmbarkStudios/cargo-deny-action@v1

.github/workflows/rust.yml

@@ -20,14 +20,14 @@ jobs:
   build-msrv:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Install Rust
         uses: dtolnay/rust-toolchain@master
         with:
           toolchain: ${{ env.msrv }}
       - name: Install sccache
-        uses: mozilla-actions/[email protected].3
+        uses: mozilla-actions/[email protected].4
 
       - name: Build libraries
         run: cargo build --workspace --exclude vise-e2e-tests --lib --all-features
@@ -37,15 +37,15 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Install Rust
         uses: dtolnay/rust-toolchain@master
         with:
           toolchain: stable
           components: rustfmt, clippy, rust-src
       - name: Install sccache
-        uses: mozilla-actions/[email protected].3
+        uses: mozilla-actions/[email protected].4
 
       - name: Format
         run: cargo fmt --all -- --check
@@ -69,14 +69,14 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Install Rust
         uses: dtolnay/rust-toolchain@master
         with:
           toolchain: ${{ env.nightly }}
       - name: Install sccache
-        uses: mozilla-actions/[email protected].3
+        uses: mozilla-actions/[email protected].4
 
       - name: Build docs
         run: |