fix: Change applicationset generate HTTP method to avoid route conflicts

[amit-o]

Closes #20757 Fixes HTTP route conflict introduced in https://github.com/argoproj/argo-cd/commit/3a5b653fb153edff37ca1460ef34d44301bf23a5 I'm not sure if PUT is the correct semantic we want here, however because /api/v1/applicationsets/{name} is already taken I wasn't sure to which route to change this to. Open to change to whatever.

If possible, would appreciate this as a hotfix to 2.13 Checklist:

• [X] Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this does not need to be in the release notes.
• [X] The title of the PR states what changed and the related issues number (used for the release note).
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• [ ] I've updated both the CLI and UI to expose my feature, or I plan to submit a second PR with them.
• [x] Does this PR require documentation updates?
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Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 55.17%. Comparing base (b39f3b1) to head (b16c036). Report is 8 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #20758 +/- ## ========================================== + Coverage 55.12% 55.17% +0.05% ========================================== Files 324 324 Lines 55256 55256 ========================================== + Hits 30458 30487 +29 + Misses 22184 22157 -27 + Partials 2614 2612 -2 ```

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[amit-o]

Thanks @andrii-korotkov-verkada, is there someone we can ping for further approval? This is a blocker for us, so I'd appreciate it if it can be hotfixed to 2.13

[andrii-korotkov-verkada]

I'll bring up the PRs marked with ready-for-review on the contributors meeting, hope they can take a look soon.