http integration tests: Migrate c_str to getStringView

[dio]

As reported in: envoyproxy/envoy#7082 (comment).

We can fix the issue by modifying https://github.com/envoyproxy/envoy-filter-example/blob/master/http-filter-example/http_filter_integration_test.cc#L39. And this PR envoyproxy/envoy#6564 for inspiration.

cc. @Satvindar

[Satvindar]

@dio, I have fixed this issue and build is successful now :)
But when I am trying to create a PR, I am getting access denied error. I am sure I am missing some configuration before I push my changes to envoy git. Can you help with the steps to follow for pushing my changes to envoy git? Thanks.

remote: Permission to envoyproxy/envoy-filter-example.git denied to Satvindar.
fatal: unable to access 'https://github.com/envoyproxy/envoy-filter-example.git/': The requested URL returned error: 403

[dio]

@Satvindar you need to work on your own fork. Please see e.g. this: https://gist.github.com/Chaser324/ce0505fbed06b947d962