When running e2e tests on flaky networks, gravatar can cause a timeout
and test failures. Turn off, and populate avatars on e2e test suite run
to make them reliable.
(cherry picked from commit 9ac74a1a408136455a9e0586fb8e65163048597b)
Conflicts:
models/fixtures/user.yml
services/repository/contributors_graph_test.go
trivial context conflicts
Unfortunately, when a system setting hasn't been stored in the database,
it cannot be cached.
Meanwhile, this PR also uses context cache for push email avatar display
which should avoid to read user table via email address again and again.
According to my local test, this should reduce dashboard elapsed time
from 150ms -> 80ms .
