feat: Add PerformanceTests

[dayaffe]

Issue #

SWIFT-2636

Description of changes

• Add PerformanceTests to the SDK, starting with a latency test on STS. Execute using swift run
• XCTest was considered but instead this is an executable for fine grained control over the output
• Test results are printed to standard out

Example Output:

{
  "productId" : "AWS SDK for Swift",
  "commitId" : "597be9d3fc7286807fd7a75c2153f6374eb9ef0c",
  "results" : [
    {
      "date" : 1743017237,
      "name" : "sts.getcalleridentity.latency",
      "unit" : "Milliseconds",
      "description" : "The total time between initiating a GetCallerIdentity and reading the last byte of the object.",
      "dimensions" : [
        {
          "name" : "OS",
          "value" : "macOS"
        }
      ],
      "measurements" : [
        358.86406898498535,
        276.1859893798828,
        285.6259346008301,
        274.4629383087158,
        279.0100574493408
      ]
    }
  ],
  "sdkVersion" : "1.2.36"
}

New/existing dependencies impact assessment, if applicable

Conventional Commits

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

[sichanyoo]

Comments mostly around naming & organization.

[jbelkins]

nit: cases of a Swift enum should start with lower case (macOS, linux, unknown)

[jbelkins]

I think we do it elsewhere, but for safety maybe trim leading & trailing whitespace before returning version string

[jbelkins]

These may as well be doc comments (three slashes on line before property) so that they show in tooltip help

Also, the same sort of comments are appropriate on PerformanceTestReport and PerformanceTestResult which also form the test report structure.