Fix: accept different types (URLs or str) as environment variables values

[Guts]

To avoid ambiguity, it adds an option to the Environment variables manager job allowing user to specify value type:

  - name: Set environment variables
    uses: manage-env-vars
    with:
      - name: HTTP_PROXY
        action: "add"
        scope: "user"
        value: "http://proxy.qdt.fr:8080"
        value_type: url
      - name: HTTPS_PROXY
        action: "add"
        scope: "user"
        value: "https://proxy.qdtfr:443"
        value_type: url
      - name: DISABLE_SSL
        action: "add"
        scope: "user"
        value: False
        value_type: bool
      - name: PYQGIS_STARTUP
        action: "add"
        scope: "user"
        value: "~/qgis/startup.py"
        value_type: path

Closes #290

[codecov-commenter]

Codecov Report

Merging #291 (76a97f6) into main (dc78dca) will decrease coverage by 3.88%.
The diff coverage is 72.50%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #291      +/-   ##
==========================================
- Coverage   64.69%   60.81%   -3.88%     
==========================================
  Files          35       36       +1     
  Lines        2042     2075      +33     
  Branches      431      440       +9     
==========================================
- Hits         1321     1262      -59     
- Misses        607      698      +91     
- Partials      114      115       +1     

Impacted Files	Coverage Δ
...loyment_toolbelt/jobs/job_environment_variables.py	53.19% <50.00%> (-33.66%)	⬇️
qgis_deployment_toolbelt/utils/url_helpers.py	87.50% <87.50%> (ø)

... and 4 files with indirect coverage changes