fix: clean up temp images created for actions with --disable-cache

[dtrudg]

When an action (run/exec/shell...) is performed against a remote image URI then it is implicitly pulled before execution.

If the cache is active, the image is pulled into the cache and executed using the image in the cache. If the cache is disabled then the image is pulled to a temporary location, and executed from there.

Prior to this PR, a temporary image pulled when the cache is disabled was not being cleaned-up on exit. This means that TMPDIR space is consumed, and not released, each time singularity is run against a remote image URI with --disable-cache.

This PR corrects the issue by:

1. Moving the implicit temporary image creation behaviour out of the client packages, into the CLI level.

2. Adding a new 'PullTempDir` value to launcher and engine configuration, which tracks the created temporary directory that must be cleaned-up on exit.

3. Adding code to the cleanup routines of the native runtime engine, and OCI launcher, to perform the actual deletion of the temp dir on container exit.

To test, run/shell/exec containers from remote (library, docker etc.) URIs with --disable-cache. During execution note that there is a /tmp/singularity-action-pull-xxxx directory containing the image, and that it is removed on container exit. The --debug output contains messages detailing this. e.g.:

$ singularity --debug run --disable-cache library://alpine
DEBUG   [U=1000,P=193493]  persistentPreRun()            Singularity version: 4.3.0+333-geb189737a
DEBUG   [U=1000,P=193493]  persistentPreRun()            Parsing configuration file /usr/local/etc/singularity/singularity.conf
DEBUG   [U=1000,P=193493]  maybeReExec()                 Checking whether to re-exec
DEBUG   [U=1000,P=193493]  handleConfDir()               /home/dtrudg-sylabs/.singularity already exists. Not creating.
DEBUG   [U=1000,P=193493]  handleRemoteConf()            Ensuring file permission of 0600 on /home/dtrudg-sylabs/.singularity/remote.yaml
DEBUG   [U=1000,P=193493]  uriToTempImage()              Cache disabled, pulling image to temporary file: /tmp/singularity-action-pull-4160879587/image
DEBUG   [U=1000,P=193493]  PullToFile()                  Cache disabled, pulling directly to: /tmp/singularity-action-pull-4160879587/image
...
Singularity> exit
...
INFO    [U=1000,P=193493]  CleanupContainer()            Cleaning up image temporary dir(s)...
VERBOSE [U=1000,P=193493]  CleanupContainer()            Removing /tmp/singularity-action-pull-4160879587
DEBUG   [U=1000,P=193493]  Master()                      Child exited with exit status 0

Fixes: #3940