docs: Document "all" as valid value in bitbucket.repositoryQuery

Created by: tsenart

Fixes #4474

Created by: tsenart

@sourcegraph/core-services: I special cased "all" as it's better UX.

Created by: codecov[bot]

Codecov Report

Merging #4475 into master will decrease coverage by 0.13%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #4475      +/-   ##
==========================================
- Coverage   47.22%   47.09%   -0.14%     
==========================================
  Files         720      718       -2     
  Lines       43564    43474      -90     
  Branches     1762     1741      -21     
==========================================
- Hits        20575    20473     -102     
- Misses      21030    21072      +42     
+ Partials     1959     1929      -30

Impacted Files	Coverage Δ
cmd/repo-updater/repos/bitbucketserver.go	82.65% <100%> (+0.3%)
cmd/frontend/graphqlbackend/discussion_comments.go	0% <0%> (-10%)
...d/frontend/internal/authz/authz_bitbucketserver.go	72.72% <0%> (-6.07%)
cmd/frontend/graphqlbackend/discussion_threads.go	8.83% <0%> (-4.45%)
cmd/frontend/db/discussion_comments.go	37.57% <0%> (-4.35%)
...rontend/internal/authz/bitbucketserver/provider.go	69.33% <0%> (-3.51%)
cmd/frontend/db/discussion_comments_mock.go	0% <0%> (ø)
web/src/routes.tsx	25.64% <0%> (ø)
cmd/frontend/db/discussion_threads_mock.go	0% <0%> (ø)
web/src/nav/StatusMessagesNavItem.tsx
... and 5 more