adding support for digest authentication

[Mzack9999]

Proposed changes

This PR adds support for HTTP Digest Authentication via the new template settings digest-username and digest-password

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)

Notes

• Depends on: Adding support for digest authentication retryablehttp-go#17
• The credentials would be better suited via HTTP Requests Annotation Prototype #1805 as the auth cookie is obtained during the initial request, and subsequent ones can benefit from shared cookiejar

Reproduction steps

$ cat digest.yaml
id: digest-test

info:
  name: digest-test
  author: digest-test
  severity: info
  reference: seh
  tags: boh

requests:
  - raw:
      - |
        GET /test HTTP/1.1
        Host: {{Hostname}}
    
    digest-username: user
    digest-password: passwd
$ echo http://httpbin.org/digest-auth/auth/user/passwd | go run . -duc -no-interactsh -t digest.yaml -debug
...
[INF] Templates loaded for scan: 1
[INF] [digest-test] Dumped HTTP request for http://httpbin.org/digest-auth/auth/user/passwd

GET /digest-auth/auth/user/passwd/test HTTP/1.1
Host: httpbin.org
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_2) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/36.0.1944.0 Safari/537.36
Connection: close
Accept-Encoding: gzip

[DBG] [digest-test] Dumped HTTP response (Truncated) http://httpbin.org/digest-auth/auth/user/passwd/test

HTTP/1.1 200 OK
Connection: close
Content-Length: 47
Access-Control-Allow-Credentials: true
Access-Control-Allow-Origin: *
Content-Type: application/json
Date: Tue, 05 Apr 2022 06:48:03 GMT
Server: gunicorn/19.9.0
Set-Cookie: fake=fake_value; Path=/

{
  "authenticated": true,
  "user": "user"
}
[INF] No results found. Better luck next time!

[ehsandeep]

GET /digest-auth/auth/user/passwd/test HTTP/1.1
Host: httpbin.org
User-Agent: Go-http-client/1.1
Authorization: Digest username="user", realm="me@kennethreitz.com", nonce="29e379f905327a31b79c022b35ee302a", uri="/digest-auth/auth/user/passwd/test", response="505c202f0680d37bbe5aec9919355e90", cnonce="662f62d9ac36ddb099fe8a3b14a92670", opaque="f151368fe26ba4e439be9f91e4890478", qop=auth, nc=00000001
Accept-Encoding: gzip, deflate
Connection: close

Custom or Random User-Agent is considered if defined in the template.