feat: add session cookie path configuration

[sgal]

Related issue(s)

Fixes #3473

Adds a configuration of a session cookie path, for setups where Hydra is served through a shared domain.

Checklist

• I have read the contributing guidelines.
• I have referenced an issue containing the design document if my change
  introduces a new feature.
• I am following the
  contributing code guidelines.
• I have read the security policy.
• I confirm that this pull request does not address a security
  vulnerability. If this pull request addresses a security vulnerability, I
  confirm that I got the approval (please contact
  security@ory.sh) from the maintainers to push
  the changes.
• I have added tests that prove my fix is effective or that my feature
  works.
• I have added or changed the documentation.

Further Comments

[codecov]

Codecov Report

Merging #3475 (31ae83a) into master (a663927) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

❗ Current head 31ae83a differs from pull request most recent head 29ceb95. Consider uploading reports for the commit 29ceb95 to get more accurate results

@@            Coverage Diff             @@
##           master    #3475      +/-   ##
==========================================
- Coverage   76.83%   76.81%   -0.02%     
==========================================
  Files         123      123              
  Lines        9125     9127       +2     
==========================================
  Hits         7011     7011              
- Misses       1666     1669       +3     
+ Partials      448      447       -1     

Impacted Files	Coverage Δ
driver/registry_base.go	85.93% <ø> (ø)
consent/strategy_default.go	69.50% <100.00%> (ø)
driver/config/provider.go	81.99% <100.00%> (+0.13%)	⬆️

... and 2 files with indirect coverage changes

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[aeneasr]

This looks good to me! For this to work though, you'll need to add this new config key to the config json schema: https://github.com/ory/hydra/blob/master/spec/config.json

[sgal]

Fixed the config and the description.