Remove ro for locally mounted folders

[atishpatel]

https://github.com/sourcegraph/src-cli/issues/1055

Remove read-only config from locally mounted folders. This gives more flexibility to locally run Batch Changes since more files can be shared as output for any step where the folder is mounted. Security should be fine since mount already has to be a sub director of the batch spec file.

[peterguy]

Thank you for the contribution, @atishpatel!

As was mentioned in #1055, there could be some security concerns mounting volumes read-write, so we should pull in @sourcegraph/security-code-review and some domain experts like @eseliger and @BolajiOlajide to get their input.

[atishpatel]

Thanks Peter!

I am curious what security vector the team is concerned about. I would think security should be fine since mount already has to be a sub director of the batch spec file and the container + code being run is also determined by the user. What are the the sourcegraph security team's concerns?

[atishpatel]

Any updates on this PR or something like this PR? My company is using rw local mounting as a core part of tooling we're building around sourcegraph batch changes