Convert flake report from Python to Go (#9334)

## What changed?
* Convert the flake report we use to monitor functional test reliability
from invoking the `tringa` cli tool and a Python script to only a Go
script that fetches the artifacts, parses the JUnit, and creates the
report.
* This also fixes an issue where `tringa` only found the last 20 tests,
the Go script will iterate through all failures in the last `N` days

## Why?
Everything is in a single executable making it easier to test and
extend.

## How did you test it?
- [X] built
- [X] run locally and tested manually
- [ ] covered by existing tests
- [X] added new unit test(s)
- [ ] added new functional test(s)

## Potential risks
Minimal, this is only a tooling change.

cmd/tools/flakereport/main.go

@@ -0,0 +1,15 @@
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"go.temporal.io/server/tools/flakereport"
+)
+
+func main() {
+	if err := flakereport.NewCliApp().Run(os.Args); err != nil {
+		fmt.Fprintf(os.Stderr, "Error running flakereport: %v\n", err)
+		os.Exit(1)
+	}
+}