feat(request): implement PUT for configmaps and add payloadSize to postDel

[xinWeiWei24]

• Wire RequestPut through requestPutBuilder; build ConfigMap body inline and PUT to /api/v1/namespaces//configmaps/. Restricted to core/v1 configmaps (validated in load_traffic.go).
• Add payloadSize to RequestPostDel; expose it as env.PAYLOAD in pod.tpl so POST'd fake pods actually carry the configured bytes.
• Add randomPayload helper (crypto/rand, [a-zA-Z0-9]).

[fuweid]

how about this?

func randomPayload(n int) string {
        if n <= 0 {
                return ""
        }

        const alphabet = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"

        // Only use byte values in [0, max). Since len(alphabet)=62 and
        // 248 is the largest multiple of 62 below 256, mapping b%62 is uniform
        // for accepted bytes. Bytes 248..255 are skipped to avoid modulo bias.
        const max = byte(256 - 256%len(alphabet))

        out := make([]byte, n)

        bufSize := n
        if bufSize > 4096 {
                bufSize = 4096
        }
        buf := make([]byte, bufSize)

        for i := 0; i < n; {
                if _, err := rand.Read(buf); err != nil {
                        panic(fmt.Errorf("failed to read random bytes: %w", err))
                }

                for _, b := range buf {
                        if b >= max {
                                continue
                        }
                        out[i] = alphabet[int(b)%len(alphabet)]
                        i++
                        if i == n {
                                return string(out)
                        }
                }
        }

        return string(out)
  }

[xinWeiWei24]

Thanks for the feedback! Updated in the latest commit, PTAL.