Cache template directory in init command

[hpmellema]

Description of changes:
Caches a copy of the smithy init template directory in the default system temp directory. This greatly speeds up subsequent executions of both the list and create template subcommands of the smithy init.
Previously, creating a template could take up to 6 seconds. With this change that time is down to ~0.3sec after the initial caching of the template repo.

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Example Executions
Create a Template

List Templates

Note: the gif recorder used here adds additional lag so these do not accurately represent the time these commands take to execute.

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[mtdowling]

rather than cache to the temp directory, I suggest caching to the build directory somewhere, allowing smithy clean to be used to clear any caches.

[mtdowling]

Is it possible to add integration tests for the added functionality of the init command?

[hpmellema]

For some reason the file lock on the .git pack files on the windows runner do not seem to be released (possibly due to the windows git file monitor?). I am working on trying to find the root cause and a fix, but in the mean time this PR will have to wait for that fix.

Update: Issue appears to actually be that git for windows marks pack files as readonly.
see this question for more context