p7519-fsmonitor: add a git add benchmark

p7519-fsmonitor: add a git add benchmark

Test                                                                     v2.29.0-rc1       this tree
-----------------------------------------------------------------------------------------------------------------
7519.2: status (fsmonitor=.git/hooks/fsmonitor-watchman)                 1.48(0.79+0.67)   1.48(0.79+0.67) +0.0%
7519.3: status -uno (fsmonitor=.git/hooks/fsmonitor-watchman)            0.16(0.11+0.05)   0.17(0.13+0.04) +6.3%
7519.4: status -uall (fsmonitor=.git/hooks/fsmonitor-watchman)           1.36(0.77+0.58)   1.37(0.72+0.63) +0.7%
7519.5: diff (fsmonitor=.git/hooks/fsmonitor-watchman)                   0.84(0.21+0.63)   0.14(0.11+0.03) -83.3%
7519.6: diff -- 0_files (fsmonitor=.git/hooks/fsmonitor-watchman)        0.12(0.07+0.05)   0.13(0.09+0.04) +8.3%
7519.7: diff -- 10_files (fsmonitor=.git/hooks/fsmonitor-watchman)       0.12(0.09+0.04)   0.13(0.07+0.06) +8.3%
7519.8: diff -- 100_files (fsmonitor=.git/hooks/fsmonitor-watchman)      0.12(0.08+0.05)   0.12(0.08+0.05) +0.0%
7519.9: diff -- 1000_files (fsmonitor=.git/hooks/fsmonitor-watchman)     0.12(0.08+0.05)   0.13(0.09+0.04) +8.3%
7519.10: diff -- 10000_files (fsmonitor=.git/hooks/fsmonitor-watchman)   0.14(0.08+0.06)   0.13(0.07+0.06) -7.1%
7519.11: add (fsmonitor=.git/hooks/fsmonitor-watchman)                   2.75(1.41+1.27)   2.03(1.26+0.70) -26.2%
7519.13: status (fsmonitor=)                                             1.38(1.03+1.04)   1.37(1.04+1.04) -0.7%
7519.14: status -uno (fsmonitor=)                                        1.11(0.83+0.98)   1.10(0.89+0.90) -0.9%
7519.15: status -uall (fsmonitor=)                                       2.30(1.57+1.42)   2.31(1.49+1.50) +0.4%
7519.16: diff (fsmonitor=)                                               1.43(1.13+1.76)   1.46(1.19+1.72) +2.1%
7519.17: diff -- 0_files (fsmonitor=)                                    0.10(0.08+0.04)   0.11(0.08+0.04) +10.0%
7519.18: diff -- 10_files (fsmonitor=)                                   0.10(0.07+0.05)   0.11(0.08+0.04) +10.0%
7519.19: diff -- 100_files (fsmonitor=)                                  0.10(0.07+0.04)   0.11(0.07+0.05) +10.0%
7519.20: diff -- 1000_files (fsmonitor=)                                 0.10(0.08+0.03)   0.11(0.08+0.04) +10.0%
7519.21: diff -- 10000_files (fsmonitor=)                                0.11(0.08+0.05)   0.12(0.07+0.06) +9.1%
7519.22: add (fsmonitor=)                                                2.26(1.46+1.49)   2.27(1.42+1.55) +0.4%

Signed-off-by: Nipunn Koorapati <nipunn@dropbox.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>