Add downstream tls configs

[AmaliMatharaarachchi]

Purpose

Issues

Fixes https://github.com/wso2/product-microgateway/issues/3468

Automation tests

• Unit tests added: No
• Integration tests added: No

Tested environments

Not Tested

---

Maintainers: Check before merge

• [x] Assigned 'Type' label
• [x] Assigned the project
• [x] Validated respective github issues
• [x] Assigned milestone to the github issue(s)

[codecov[bot]]

Codecov Report

Attention: 8 lines in your changes are missing coverage. Please review.

Comparison is base (dcb096d) 27.55% compared to head (d292f8e) 27.60%. Report is 114 commits behind head on main.

Files	Patch %	Lines
adapter/internal/oasparser/envoyconf/listener.go	70.37%	7 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #3469 +/- ## ============================================ + Coverage 27.55% 27.60% +0.04% + Complexity 3374 3373 -1 ============================================ Files 483 484 +1 Lines 51822 52053 +231 Branches 6336 6350 +14 ============================================ + Hits 14281 14368 +87 - Misses 36146 36282 +136 - Partials 1395 1403 +8 ```

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