draft: IX Bid Adapter: change outgoing exchange request type from GET to POST

[ix-peiyuan]

Type of change

• [ ] Bugfix
• [x] Feature
• [ ] New bidder adapter
• [ ] Code style update (formatting, local variables)
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [ ] CI related changes
• [ ] Does this change affect user-facing APIs or examples documented on http://prebid.org?
• [ ] Other

Description of change

(The PR is a replicate of #8658, whose owned is on vacation and I am taking over)

Changes Adapter request to Exchange from GET to POST to have higher request size limit. No functional changes for users Tests updated

Contact [email protected] for more information.

[ChrisHuie]

@ix-peiyuan looks like there is a linting error here but the code it is referring to looks to be removed?