Add basic Web endpoint tests

• Added basic tests from further investigation of the endpoint gaps.
• Web endpoints threshold is 10%, except for Commits and Branches page - theses endpoints have known issues.
• Additionally added http-debug flag to be able to turn on k6 HTTP debugging. It is handy to debug web endpoints and request responses.

Test documentation with new web endpoints:

WEB

TEST	ENDPOINT	DESCRIPTION	TYPE
web_group_html.js	GET /:group	Web - Group page. Controllers: GroupsController#index	web
web_project_branches_html.js	GET /:group/:project/-/branches	Web - Project Branches page. Controllers: BranchesController	web
web_project_commits_html.js	GET /:group/:project/commits/:branch	Web - Project Commits page. Controllers: CommitsController	web
web_project_html.js	GET /:group/:project	Web - Project page. Controllers: ProjectsController#show, RefsController#logs_tree, BlobController#show	web
web_project_merge_requests_html.js	GET /:group/:project/merge_requests	Web - Project Merge Requests page. Controllers: Projects::MergeRequestsController	web
web_project_pipelines_html.js	GET /:group/:project/pipelines	Web - Project Pipelines page. Controllers: Projects::PipelinesController	web
web_project_tree_html.js	GET /:group/:project/tree/master	Web - Project Repository Files page on master branch. Controllers: Projects::TreeController	web
web_projects_blob_controller_show_html.js	GET /:group/:project/blob/master/:file_path	Web - Projects Blob Controller Show HTML	web