feat: make custom accept header is created in appInner.mustache

[jongsunpark-omelet]

    {{#hasProduces}}
            localVarHeaderParameter['Accept'] = {{#produces}}'{{{mediaType}}}'{{^-last}}; {{/-last}}{{/produces}};
    {{/hasProduces}}

이 부분만 추가하고 빌드 돌림.

[wing328]

there shouldn't be changes to the java samples.

i'll clean that up in another pr

[wing328]

filed #22318 instead

closing this one

btw, your suggested fix won't work with operations with multiple accept headers.

i've fixed that in my pr. please have a look and test the change locally when you've time.

thanks again for the contribution.