vlan: add vlan.id keyword - v3

[AkakiAlice]

Ticket: #1065

Make sure these boxes are checked accordingly before submitting your Pull Request -- thank you.

Contribution style:

• I have read the contributing guide lines at
  https://docs.suricata.io/en/latest/devguide/contributing/contribution-process.html

Our Contribution agreements:

• I have signed the Open Information Security Foundation contribution agreement at
  https://suricata.io/about/contribution-agreement/ (note: this is only required once)

Changes (if applicable):

• I have updated the User Guide (in doc/userguide/) to reflect the changes made
• I have updated the JSON schema (in etc/schema.json) to reflect all logging changes
  (including schema descriptions)
• I have created a ticket at
  https://redmine.openinfosecfoundation.org/projects/suricata/issues

Link to ticket: https://redmine.openinfosecfoundation.org/issues/1065

Describe changes:

• Introduce vlan.id keyword

Provide values to any of the below to override the defaults.

• To use an LibHTP, Suricata-Verify or Suricata-Update pull request,
  link to the pull request in the respective _BRANCH variable.
• Leave unused overrides blank or remove.

SV_BRANCH= OISF/suricata-verify#2183
Previous PR= #12103

[catenacyber]

Thanks for the work Alice

CI : red, could you investigate ?
Code : looking into it now
Commits segmentation : ok
Commit messages : title could be detect: add vlan.id keyword
Git ID set : looks fine for me
CLA : you already contributed
Doc update : good, some remark inline
Redmine ticket : ok
Rustfmt : looks ok for vlan_id.rs
Tests : nice, thanks, added a remark there
Dependencies added: none

[catenacyber]

@jasonish do you have proposals for better rust style here ?

[jasonish]

I probably would have done something like:

let du16 = if let Ok(du16) = detect_parse_uint::<u16>(parts[0]) {
    du16
} else {
    return None;
};

Even tho it's not really shorter, but does remove the unwraps.

But just today I learned that you can use ? on Option return types which lets us replace:

    let du16 = detect_parse_uint(parts[0]);
    if du16.is_err() {
        return None;
    }
    let du16 = du16.unwrap().1;

with

let du16 = detect_parse_uint(parts[0]).ok()?.1;

[jufajardini]

Shared some comments to help with the docs, mostly. ^^

We're missing adding the new file to doc/userguide/rules/index.rst, too, otherwise it won't be added, and the docs won't be generated, throwing an error.