Change target test file and add File Blame tests

Closes #243 (closed) #80 (closed)

Relates https://gitlab.com/gitlab-org/quality/performance/-/issues/244

MR changes the target file in our test data to be a notably larger one (16kb to 640kb) and also adds in tests for File Blame.

█ Results summary

* Environment:                10k
* Environment Version:        13.0.0-pre `f99438802d0`
* Option:                     60s_200rps
* Date:                       2020-05-13
* Run Time:                   6m 43.87s (Start: 11:25:59 UTC, End: 11:32:43 UTC)
* GPT Version:                v1.3.0

NAME                                        | RPS   | RPS RESULT           | TTFB AVG   | TTFB P90            | REQ STATUS     | RESULT
--------------------------------------------|-------|----------------------|------------|---------------------|----------------|------------------
api_v4_projects_repository_files_file       | 200/s | 193.92/s (>160.00/s) | 132.03ms   | 169.65ms (<500ms)   | 100.00% (>95%) | Passed
api_v4_projects_repository_files_file_blame | 200/s | 7.7/s (>160.00/s)    | 17473.52ms | 24381.81ms (<500ms) | 100.00% (>95%) | FAILED²³
api_v4_projects_repository_files_file_raw   | 200/s | 178.82/s (>160.00/s) | 214.20ms   | 169.67ms (<500ms)   | 100.00% (>95%) | Passed
web_project_file                            | 20/s  | 12.07/s (>16.00/s)   | 1571.11ms  | 3228.98ms (<500ms)  | 100.00% (>95%) | FAILED²³
web_project_file_blame                      | 20/s  | 1.0/s (>16.00/s)     | 16818.68ms | 17623.31ms (<750ms) | 100.00% (>95%) | FAILED³