add support for UUID v7 in RequestId (#116)

* feat(request_id): add support for UUID v7 in `RequestId`

feature flag `uuid_v7` is introduced which inturn enables `v7` feature flag in the `uuid` dependency
Support documentation is added in `README.md`, `src/lib.rs` and `src/request_id.rs`

This feature only works if this crate or any crate dependent on this crate has enabled the compile time configuration flag provided to the rust compiler. `RUSTFLAGS="--cfg uuid_unstable"`.

* chore: add github action to test UUID v7 feature flag

* chore: add the uuid_unstable cfg in the request id impl

* chore: add compiler_error for undesired state in configuration flags

* chore: move the compiler error in request_id module

* chore: fix formatting

* fix(action): fix github action for uuid_v7 with RUSTDOCFLAGS

.github/workflows/general.yml

@@ -77,6 +77,33 @@ jobs:
           command: test
           args: --features ${{ matrix.otel_version }}
 
+  test_uuid_v7:
+    name: Test
+    runs-on: ubuntu-latest
+    env:
+      RUSTFLAGS: "--cfg uuid_unstable"
+      RUSTDOCFLAGS: "--cfg uuid_unstable"
+    steps:
+      - uses: actions/checkout@v2
+      - name: Cache dependencies
+        id: cache-dependencies
+        uses: actions/cache@v2
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+            target
+          key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: stable
+          override: true
+      - uses: actions-rs/cargo@v1
+        with:
+          command: test
+          args: --features uuid_v7
+
   fmt:
     name: Rustfmt
     runs-on: ubuntu-latest