[BugFix] Fix Header casing of DocumentServiceResponse to be case insensitve header comparison

[visridha]

Http Headers are by default case insensitive. Fix DocumentServiceResponse so that the headers coming out of it are case insensitive.

[kirankumarkolli]

@moderakh are there any other headers implementations inside which needs attenton?

[moderakh]

There is ~5% perf impact associated to this PR:

1000
master:
2020-08-10 18:43:08,459 [main] INFO com.microsoft.azure.cosmosdb.benchmark.AsyncReadBenchmark - [2000000] operations performed in [138] seconds.
2020-08-10 18:48:45,388 [main] INFO com.microsoft.azure.cosmosdb.benchmark.AsyncReadBenchmark - [2000000] operations performed in [137] seconds.
2020-08-10 18:55:45,355 [main] INFO com.microsoft.azure.cosmosdb.benchmark.AsyncReadBenchmark - [2000000] operations performed in [143] seconds.
2020-08-10 19:03:45,723 [main] INFO com.microsoft.azure.cosmosdb.benchmark.AsyncReadBenchmark - [2000000] operations performed in [140] seconds.
2020-08-10 19:16:37,263 [main] INFO com.microsoft.azure.cosmosdb.benchmark.AsyncReadBenchmark - [2000000] operations performed in [137] seconds.
2020-08-10 19:23:03,312 [main] INFO com.microsoft.azure.cosmosdb.benchmark.AsyncReadBenchmark - [2000000] operations performed in [141] seconds.
2020-08-10 19:29:33,274 [main] INFO com.microsoft.azure.cosmosdb.benchmark.AsyncReadBenchmark - [2000000] operations performed in [135] seconds.
2020-08-10 19:34:57,802 [main] INFO com.microsoft.azure.cosmosdb.benchmark.AsyncReadBenchmark - [2000000] operations performed in [134] seconds.
2020-08-10 19:37:34,646 [main] INFO com.microsoft.azure.cosmosdb.benchmark.AsyncReadBenchmark - [2000000] operations performed in [136] seconds.

(138 + 137 + 143 + 140 + 137 + 141 + 135 + 134 + 136) throwing out the worst one 143
(138 + 137 + 140 + 137 + 141 + 135 + 134 + 136) / 8 = 137

this PR:
2020-08-10 18:37:43,643 [main] INFO com.microsoft.azure.cosmosdb.benchmark.AsyncReadBenchmark - [2000000] operations performed in [143] seconds.
2020-08-10 18:46:05,978 [main] INFO com.microsoft.azure.cosmosdb.benchmark.AsyncReadBenchmark - [2000000] operations performed in [143] seconds
2020-08-10 18:51:53,919 [main] INFO com.microsoft.azure.cosmosdb.benchmark.AsyncReadBenchmark - [2000000] operations performed in [142] seconds
2020-08-10 18:58:46,597 [main] INFO com.microsoft.azure.cosmosdb.benchmark.AsyncReadBenchmark - [2000000] operations performed in [142] seconds.
2020-08-10 19:09:56,838 [main] INFO com.microsoft.azure.cosmosdb.benchmark.AsyncReadBenchmark - [2000000] operations performed in [147] seconds.
2020-08-10 19:19:55,376 [main] INFO com.microsoft.azure.cosmosdb.benchmark.AsyncReadBenchmark - [2000000] operations performed in [148] seconds.
2020-08-10 19:26:18,030 [main] INFO com.microsoft.azure.cosmosdb.benchmark.AsyncReadBenchmark - [2000000] operations performed in [143] seconds.
2020-08-10 19:40:50,892 [main] INFO com.microsoft.azure.cosmosdb.benchmark.AsyncReadBenchmark - [2000000] operations performed in [141] seconds
2020-08-10 19:44:06,982 [main] INFO com.microsoft.azure.cosmosdb.benchmark.AsyncReadBenchmark - [2000000] operations performed in [143] seconds.

(143 + 143 + 142 + 142 + 147 + 148 + 143 + 141 + 143) throwing out the worst one 148

(143 + 143 + 142 + 142 + 147 + 143 + 141 + 143) /8 = 143

perf impact

(143 - 137)/ 137 ~ 5%