Enabling numContextLines in non-json format

[po3rin]

This PR makes NumContextLines available in formats other than json.

Why

Currently, I want to run my own search UI template on zoekt-webserver. However, since NumContextLines is only available in json format, I cannot use that information in my own template.

Please let us know what do you think. Thank you!

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[keegancsmith]

Thanks.

[po3rin]

thanks!