Add benchmark workflow (#153)

*Issue #, if available:*

*Description of changes:*
This PR builds off of PR #122 and creates a benchmark workflow similar
to integration tests workflow that runs the benchmarks added in PR #122

Add two basic benchmarks
- One that performs cache hit retrievals
- One that intentionally yields cache misses on every retrieval

Using [criterion](https://docs.rs/criterion/latest/criterion/) (used by
the AWS SDK for Rust).

This hopefully will serve to catch performance regressions in future
code changes and open the door to profiling.

Successful run from fork:
https://github.com/reyhankoyun/aws-secretsmanager-agent/actions/runs/20082405961/job/57612354790

By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 license.

---------

Signed-off-by: Simon Marty <simon.marty@protonmail.com>
Co-authored-by: Simon <simon.marty0@gmail.com>
Co-authored-by: Simon Marty <martysi@amazon.com>
Co-authored-by: Simon Marty <simon.marty@protonmail.com>

Author: reyhankoyun

.github/workflows/benchmarks.yml

@@ -0,0 +1,41 @@
+name: Benchmarks
+
+on:
+  workflow_dispatch:
+  push:
+    branches: ["main"]
+  pull_request:
+    branches: ["main"]
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  benchmark:
+    runs-on: ubuntu-latest
+    
+    permissions:
+      contents: read
+    
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v5
+    
+    - name: Install Rust stable
+      uses: actions-rs/toolchain@v1
+      with:
+        toolchain: stable
+        override: true
+    
+    - name: Run benchmarks
+      working-directory: aws_secretsmanager_caching
+      run: cargo bench --bench benchmark
+    
+    - name: Upload benchmark results
+      if: always()
+      uses: actions/upload-artifact@v4
+      with:
+        name: benchmark-results-${{ github.sha }}
+        path: target/criterion/
+        if-no-files-found: error
+        retention-days: 30