feat: [OCISDEV-1565] remove the posix driver - #774

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Please, include a link to the documentation since this must be there.
We must include:

• Migration strategy. Whether it's a "run this command" or "run a new installation and move everything there".
• I see in the 8.2 docs that the support is experimental, but I don't think that's enough to be considered as deprecated. I'm not sure if it was clear that we would officially drop support for that driver.

Do we also need some safety mechanism to prevent people from getting stuck? I mean, posix people will likely upgrade and end up with an unusable installation (not sure about up to what degree). It would be nice to have some detection and provide meaningful instructions if people reach that point.

Bluntly removing the driver will likely cause headaches. At least we need a plan to move people forward.

Please, include a link to the documentation since this must be there. We must include:

• Migration strategy. Whether it's a "run this command" or "run a new installation and move everything there".
• I see in the 8.2 docs that the support is experimental, but I don't think that's enough to be considered as deprecated. I'm not sure if it was clear that we would officially drop support for that driver.

Do we also need some safety mechanism to prevent people from getting stuck? I mean, posix people will likely upgrade and end up with an unusable installation (not sure about up to what degree). It would be nice to have some detection and provide meaningful instructions if people reach that point.

Bluntly removing the driver will likely cause headaches. At least we need a plan to move people forward.

You are absolutely right. We should include the deprecation notice in 8.2.x and provide instructions about migration.
https://owncloud.dev/ocis/guides/migrate-data-rclone/
@kobergj Is this the only way to migrate from PosixFS to DecomposedFS that we want to provide, right?