Leaving a trailing slash in the context option causes the jira-ruby
gem to add an extra slash in HTTP requests to the URL, preventing
JIRA from working properly.

Closes #42494

Signed-off-by: NRémy Coutable <remy@rymai.me>

Remove superfluous lib: true, type: redis, service: true, models: true, services: true, no_db: true, api: true
Signed-off-by: NRémy Coutable <remy@rymai.me>

The implicit interface of project services states that the "execute"
method is meant to be called when project hooks are executed.
Currently JiraService does not support any project events even though
JiraService#supported_events says that "commit" and "merge_request"
are supported. They are only used to render correct options in
JIRA configuration screen, but they are not supported.
Because of that, this commit makes "execute" method a no-op.

Signed-off-by: NRémy Coutable <remy@rymai.me>

Code improvements, bug fixes, finish documentation and specs

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5620#note_13671791

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5620#note_13540099