add multipart/form-data client support

[codecov[bot]]

Codecov Report

Patch coverage: 64.93% and project coverage change: -0.88% :warning:

Comparison is base (05c17d1) 79.82% compared to head (f603cc5) 78.94%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #64 +/- ## ============================================ - Coverage 79.82% 78.94% -0.88% - Complexity 849 875 +26 ============================================ Files 42 45 +3 Lines 3013 3187 +174 Branches 453 472 +19 ============================================ + Hits 2405 2516 +111 - Misses 445 503 +58 - Partials 163 168 +5 ``` | [Files Changed](https://app.codecov.io/gh/davidmoten/openapi-codegen/pull/64?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Dave+Moten) | Coverage Δ | | |---|---|---| | [...avidmoten/oa3/codegen/generator/ExtensionKeys.java](https://app.codecov.io/gh/davidmoten/openapi-codegen/pull/64?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Dave+Moten#diff-b3BlbmFwaS1jb2RlZ2VuLWdlbmVyYXRvci9zcmMvbWFpbi9qYXZhL29yZy9kYXZpZG1vdGVuL29hMy9jb2RlZ2VuL2dlbmVyYXRvci9FeHRlbnNpb25LZXlzLmphdmE=) | `0.00% <0.00%> (ø)` | | | [.../org/davidmoten/oa3/codegen/http/HttpResponse.java](https://app.codecov.io/gh/davidmoten/openapi-codegen/pull/64?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Dave+Moten#diff-b3BlbmFwaS1jb2RlZ2VuLWh0dHAvc3JjL21haW4vamF2YS9vcmcvZGF2aWRtb3Rlbi9vYTMvY29kZWdlbi9odHRwL0h0dHBSZXNwb25zZS5qYXZh) | `25.92% <0.00%> (-1.00%)` | :arrow_down: | | [.../oa3/codegen/http/NotPrimaryResponseException.java](https://app.codecov.io/gh/davidmoten/openapi-codegen/pull/64?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Dave+Moten#diff-b3BlbmFwaS1jb2RlZ2VuLWh0dHAvc3JjL21haW4vamF2YS9vcmcvZGF2aWRtb3Rlbi9vYTMvY29kZWdlbi9odHRwL05vdFByaW1hcnlSZXNwb25zZUV4Y2VwdGlvbi5qYXZh) | `0.00% <0.00%> (ø)` | | | [...va/org/davidmoten/oa3/codegen/http/Serializer.java](https://app.codecov.io/gh/davidmoten/openapi-codegen/pull/64?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Dave+Moten#diff-b3BlbmFwaS1jb2RlZ2VuLWh0dHAvc3JjL21haW4vamF2YS9vcmcvZGF2aWRtb3Rlbi9vYTMvY29kZWdlbi9odHRwL1NlcmlhbGl6ZXIuamF2YQ==) | `0.00% <0.00%> (ø)` | | | [...davidmoten/oa3/codegen/http/DefaultSerializer.java](https://app.codecov.io/gh/davidmoten/openapi-codegen/pull/64?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Dave+Moten#diff-b3BlbmFwaS1jb2RlZ2VuLWh0dHAvc3JjL21haW4vamF2YS9vcmcvZGF2aWRtb3Rlbi9vYTMvY29kZWdlbi9odHRwL0RlZmF1bHRTZXJpYWxpemVyLmphdmE=) | `20.00% <11.11%> (-5.93%)` | :arrow_down: | | [...ain/java/org/davidmoten/oa3/codegen/http/Http.java](https://app.codecov.io/gh/davidmoten/openapi-codegen/pull/64?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Dave+Moten#diff-b3BlbmFwaS1jb2RlZ2VuLWh0dHAvc3JjL21haW4vamF2YS9vcmcvZGF2aWRtb3Rlbi9vYTMvY29kZWdlbi9odHRwL0h0dHAuamF2YQ==) | `58.12% <11.11%> (-10.30%)` | :arrow_down: | | [...oa3/codegen/generator/writer/ClientCodeWriter.java](https://app.codecov.io/gh/davidmoten/openapi-codegen/pull/64?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Dave+Moten#diff-b3BlbmFwaS1jb2RlZ2VuLWdlbmVyYXRvci9zcmMvbWFpbi9qYXZhL29yZy9kYXZpZG1vdGVuL29hMy9jb2RlZ2VuL2dlbmVyYXRvci93cml0ZXIvQ2xpZW50Q29kZVdyaXRlci5qYXZh) | `95.95% <50.00%> (+0.08%)` | :arrow_up: | | [...ava/org/davidmoten/oa3/codegen/http/MediaType.java](https://app.codecov.io/gh/davidmoten/openapi-codegen/pull/64?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Dave+Moten#diff-b3BlbmFwaS1jb2RlZ2VuLWh0dHAvc3JjL21haW4vamF2YS9vcmcvZGF2aWRtb3Rlbi9vYTMvY29kZWdlbi9odHRwL01lZGlhVHlwZS5qYXZh) | `45.45% <50.00%> (+12.12%)` | :arrow_up: | | [...rg/davidmoten/oa3/codegen/http/ParameterValue.java](https://app.codecov.io/gh/davidmoten/openapi-codegen/pull/64?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Dave+Moten#diff-b3BlbmFwaS1jb2RlZ2VuLWh0dHAvc3JjL21haW4vamF2YS9vcmcvZGF2aWRtb3Rlbi9vYTMvY29kZWdlbi9odHRwL1BhcmFtZXRlclZhbHVlLmphdmE=) | `77.27% <62.50%> (-2.73%)` | :arrow_down: | | [...n/oa3/codegen/generator/ClientServerGenerator.java](https://app.codecov.io/gh/davidmoten/openapi-codegen/pull/64?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Dave+Moten#diff-b3BlbmFwaS1jb2RlZ2VuLWdlbmVyYXRvci9zcmMvbWFpbi9qYXZhL29yZy9kYXZpZG1vdGVuL29hMy9jb2RlZ2VuL2dlbmVyYXRvci9DbGllbnRTZXJ2ZXJHZW5lcmF0b3IuamF2YQ==) | `82.88% <76.31%> (-0.04%)` | :arrow_down: | | ... and [9 more](https://app.codecov.io/gh/davidmoten/openapi-codegen/pull/64?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Dave+Moten) | |

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