Pod 763/ expose execute timeout as context option

[bkneis]

This PR fixes POD-763 by providing a new context option EXECUTE_TIMEOUT to set the timeout in seconds, instead of a hard coded value.

To test this PR I have run ./devpod-cli up examples/simple to ensure injecting the binary still works, I also ran ./devpod-cli context options to ensure the option is listed and ./devpod-cli context set-options default -o EXECUTE_TIMEOUT=60 to ensure it can be updated.