fix browser WPS XML response content-type resolution

[fmigneault]

Fixes

• Fix default XML format resolution for WPS endpoint when no Accept header or format/f query parameter is provided and that the request is submitted from a Web Browser, which involves additional control logic to select the applicable Content-Type for the response.

Browser WPS XML response auto-redirected to JSON caused an unresolved process description when submitted from the browser.

[codecov[bot]]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (e5f79a5) 85.18% compared to head (80d1c48) 85.17%.

Files	Patch %	Lines
weaver/formats.py	33.33%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #591 +/- ## ========================================== - Coverage 85.18% 85.17% -0.02% ========================================== Files 79 79 Lines 18023 18023 Branches 2728 2728 ========================================== - Hits 15353 15351 -2 - Misses 1940 1941 +1 - Partials 730 731 +1 ```

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