Unify intracluster sync and Drydock working copy construction timeouts as a repository "copy time limit"

Summary:
Depends on D19814. Ref T13216. See PHI885. For various eldritch reasons, `git fetch` can hang. Although we'd probably like to fix this with `git fetch --require-sustained-network-transfer-rate=512KB/5s` or similar, that flag doesn't exist and we don't have a reasonable way to build it.

Short of that, move toward formalizing a repository "copy time limit": the longest amount of time anything may spend trying to make a copy of this repository.

This grows out of the existing intracluster sync limit, which is effectively the same thing. Here, apply it to `git clone` and `git fetch` in Drydock working copy construction, too. A future change may make it configurable.

Test Plan:
  - Set the limit to 0.001.
  - Tried to build and lease working copies, got sensible timeout errors (see D19815).

```
<Activation Failed> Lease activation failed: [CommandException] Command killed by timeout after running for more than 0.001 seconds.
COMMAND
ssh '-o' 'LogLevel=quiet' '-o' 'StrictHostKeyChecking=no' '-o' 'UserKnownHostsFile=/dev/null' '-o' 'BatchMode=yes' -l '********' -p '2222' -i '********' '127.0.0.1' -- '(cd '\''/var/drydock/workingcopy-163/repo/spellbook/'\'' && git clean -d --force && git fetch && git reset --hard)'
```

Reviewers: amckinley

Reviewed By: amckinley

Subscribers: yelirekim, PHID-OPKG-gm6ozazyms6q6i22gyam

Maniphest Tasks: T13216

Differential Revision: https://secure.phabricator.com/D19816