remove use of iterate() in flow

[tarunKoyalwar]

Proposed changes

• Earlier it was required to use iterate function in flow when it is unknown if array contains one or more value due to flattening of single value array's to string
• this is now fixed by preserving array type in flow and flattening at protocol level instead of doing it in flow
• added integration test for this case
• closes fix iteration in flow if array contained only 1 value #4689

Checklist

• Pull request is created against the dev branch
• All checks passed (lint, unit/integration/regression tests etc.) with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

[tarunKoyalwar]

example template

id: flow-iterate-one-value-flow

info:
  name: Test Flow Iterate One Value Flow
  author: pdteam
  severity: info

flow: |
  http(1)
  for(let value of template.extracted){
    set("value", value)
    http(2)
  }
http:
  - method: GET
    path:
      - "{{BaseURL}}"

    extractors:
      - type: regex
        name: extracted
        internal: true
        regex:
          - "[ok]+"

  - method: GET
    path:
      - "{{BaseURL}}/{{value}}"

    matchers:
      - type: word
        words:
          - "ok"

Incorrect behaviour ( in latest nuclei)

• if one value was extracted then nuclei was iterating over each character

$ nuclei -u scanme.sh -t integration_tests/flow/iterate-one-value-flow.yaml 

                     __     _
   ____  __  _______/ /__  (_)
  / __ \/ / / / ___/ / _ \/ /
 / / / / /_/ / /__/ /  __/ /
/_/ /_/\__,_/\___/_/\___/_/   v3.1.7

		projectdiscovery.io

[INF] Current nuclei version: v3.1.7 (latest)
[INF] Current nuclei-templates version: v9.7.4 (latest)
[WRN] Scan results upload to cloud is disabled.
[INF] New templates added in latest release: 6
[INF] Templates loaded for current scan: 1
[WRN] Executing 1 unsigned templates. Use with caution.
[INF] Targets loaded for current scan: 1
[INF] Running httpx on input host
[INF] Found 1 URL from httpx
[flow-iterate-one-value-flow] [http] [info] https://scanme.sh/o
[flow-iterate-one-value-flow] [http] [info] https://scanme.sh/k

After fix / this PR

$ ./nuclei -u scanme.sh -t integration_tests/flow/iterate-one-value-flow.yaml

                     __     _
   ____  __  _______/ /__  (_)
  / __ \/ / / / ___/ / _ \/ /
 / / / / /_/ / /__/ /  __/ /
/_/ /_/\__,_/\___/_/\___/_/   v3.1.7

		projectdiscovery.io

[INF] Current nuclei version: v3.1.7 (latest)
[INF] Current nuclei-templates version: v9.7.4 (latest)
[WRN] Scan results upload to cloud is disabled.
[INF] New templates added in latest release: 6
[INF] Templates loaded for current scan: 1
[WRN] Executing 1 unsigned templates. Use with caution.
[INF] Targets loaded for current scan: 1
[INF] Running httpx on input host
[INF] Found 1 URL from httpx
[flow-iterate-one-value-flow] [http] [info] https://scanme.sh/ok