Elements now have the ability to be required on pages or not
Currently using the default wait mechanism
Altered the ElementWithPattern Cop to fit new splat for init

These are very high-level. Currently, they test:

1. That the performance bar appears.
2. That it has detailed metrics for Postgres and Gitaly.
3. That AJAX requests are included in the request selector.

First attempt at allowing a feature flag to be set via the command line
when running tests. This will enable the flag, run the tests, and then
disable the flag.

Using OptionParser meant changing how scenarios get the instance
address, so this also allows the address to be set as a command line
option. It's backwards compatible (you can still provide the address
as the command line option after the scenario)

Add "smoke" tag to the test

Fix links to views in Page Object files

Review fixes

Remove useless view block

Implement Snippets::Show page object class

Fix review suggestions

Fix review suggestions 2

Fix test with empty snippets state

Remove useless css class

Fix issues

This avoids running before/after blocks for tests that are in quarantine

Add tag validation on pipeline page

Also use refactor retry_on_excpetion and use it in select_*_filter
methods

Adds the test itself and the vendor page object model for GitHub
login pages.