Hidden manifests implementation (new)

[Hook25]

Description

We need a “hidden” manifest type to be able to include/exclude jobs runs in the lab without impact normal end user experience:

Hidden = not available for general consumption, not shown in the Manifest entries screen

hidden keyword raises questions, so need an additional hidden_reason field to explain why this manifest is not shown to the user (e.g. “No OBEX server testing required in the HW Cert lab”)

These manifest entries must be false (i.e. not set) for submissions made to issue a Certificate (Cert issuance process must include this check, this is a critical violation because it can lead to important things not being tested)

Hidden manifest IDs must start with _ (underscore). This is for easier reading/parsing/debugging, and must have a hidden-reason field to explain why they were introduced.

Resolved issues

Fixes: CHECKBOX-1698

Documentation

New field documented in reference

Tests

Tested via metabox + unittest

[codecov]

Codecov Report

Attention: Patch coverage is 93.10345% with 4 lines in your changes missing coverage. Please review.

Project coverage is 49.12%. Comparing base (6e0aee0) to head (5acfc82).
Report is 11 commits behind head on main.

Files with missing lines	Patch %	Lines
checkbox-ng/plainbox/impl/session/assistant.py	93.33%	2 Missing and 1 partial ⚠️
checkbox-ng/checkbox_ng/launcher/subcommands.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1699      +/-   ##
==========================================
+ Coverage   49.01%   49.12%   +0.10%     
==========================================
  Files         372      372              
  Lines       40348    40338      -10     
  Branches     6817     6809       -8     
==========================================
+ Hits        19777    19816      +39     
+ Misses      19849    19799      -50     
- Partials      722      723       +1     

Flag	Coverage Δ
checkbox-ng	69.70% <93.10%> (+0.30%)	⬆️

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[fernando79513]

Good job, Max!
The PR looks good to me. The hidden manifest implementation is what we've discussed previously and the renamings here and there look coherent.
Also, the metabox tests seem to cover the functionality properly.
I've left a small comment if you fancy to change it, but I leve it to you.