Update map-query-parameters.md

[offtherailz]

Description

With this PR we improve the query parameter sample to provide the support for get/post map also via iframe

Please check if the PR fulfills these requirements

• [x] The commit message follows our guidelines: https://github.com/geosolutions-it/MapStore2/blob/master/CONTRIBUTING.md
• [x] Tests for the changes have been added (for bug fixes / features)
• [x] Docs have been added / updated (for bug fixes / features)

What kind of change does this PR introduce? (check one with "x", remove the others)

• [ ] Bugfix
• [ ] Feature
• [ ] Code style update (formatting, local variables)
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [ ] CI related changes
• [x] Other... Please describe: Documentation

Issue

What is the current behavior? #8393

What is the new behavior? Post now works with iframe, this helps to test the functionality

Breaking change

Does this PR introduce a breaking change? (check one with "x", remove the other)

• [ ] Yes, and I documented them in migration notes
• [x] No

Other useful information