This fixes a vulnerability with the `CODER_OIDC_EMAIL_DOMAIN` option,
where users with a superset of the allowed email domain would be allowed
to login. For example, given `CODER_OIDC_EMAIL_DOMAIN=google.com`, a
user would be permitted entry if their email domain was
`colin-google.com`.

(cherry picked from commit 4439a92)

* fix: do not set max deadline for workspaces on template update

When templates are updated and schedule data is changed, we update all
running workspaces to have up-to-date scheduling information that sticks
to the new policy.

When updating the max_deadline for existing running workspaces, if the
max_deadline was before now()+2h we would set the max_deadline to
now()+2h.

Builds that don't/shouldn't have a max_deadline have it set to 0, which
is always before now()+2h, and thus would always have the max_deadline
updated.

* test: add unit test to excercise template schedule bug
---------

Co-authored-by: Steven Masley <stevenmasley@gmail.com>

- Reworks the proxy registration loop into a struct (so I can add a `RegisterNow` method)
- Changes the proxy registration loop interval to 15s (previously 30s)
- Adds test which tests bidirectional DERP meshing on all possible paths between 6 workspace proxy replicas

Related to coder/customers#438

…#12178)

* fix: add future-proofing for clipboard copies on http connections

* docs: clean up comment formatting