Add exact_title filter to findings API

[brammie15]

Description

This PR adds a new optional query parameter exact_title to the /api/v2/findings endpoint to allow exact title matching.

Existing behavior remains unchanged:

• title filter continues to use loose substring matching (icontains)
  New behavior:
• exact_title filter performs an exact match on Finding.title (case-insensitive, iexact)

Example:
GET /api/v2/findings?exact_title=TLS%20Certificate%20Expired

Test results

Ideally you extend the test suite in tests/ and dojo/unittests to cover the changed in this PR.
Alternatively, describe what you have and haven't tested.

Manual testing using local DefectDojo docker-compose environment:

• Verified GET /api/v2/findings?exact_title= returns only the finding(s) with that exact title
• Verified GET /api/v2/findings?title= still returns substring matches (unchanged)

Documentation

OpenAPI should include it via django-filter introspection; verified in swagger UI locally

Checklist

This checklist is for your information.

• Make sure to rebase your PR against the very latest dev.
• Features/Changes should be submitted against the dev.
• [] Bugfixes should be submitted against the bugfix branch.
• Give a meaningful name to your PR, as it may end up being used in the release notes.
• [] Your code is Ruff compliant (see ruff.toml).
• Your code is python 3.13 compliant.
• If this is a new feature and not a bug fix, you've included the proper documentation in the docs at https://github.com/DefectDojo/django-DefectDojo/tree/dev/docs as part of this PR.
• Model changes must include the necessary migrations in the dojo/db_migrations folder.
• Add applicable tests to the unit tests.
• Add the proper label to categorize your PR.

[dryrunsecurity]

This pull request modifies a sensitive file path (dojo/filters.py) flagged by the configured codepaths scanner as a sensitive edit; reviewers should verify the change or update .dryrunsecurity.yaml to allow this author/path.

🔴 Configured Codepaths Edit in dojo/filters.py (drs_be90788e)

Vulnerability	Configured Codepaths Edit
Description	Sensitive edits detected for this file. Sensitive file paths and allowed authors can be configured in .dryrunsecurity.yaml.

We've notified @mtesauro.

---

Comment to provide feedback on these findings.

Report false positive: @dryrunsecurity fp [FINDING ID] [FEEDBACK]
Report low-impact: @dryrunsecurity nit [FINDING ID] [FEEDBACK]

Example: @dryrunsecurity fp drs_90eda195 This code is not user-facing

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