Add cleanup subcommand to remove older tool versions

[givaldolins]

Problem
Over time, backplane-tools accumulates multiple versions of each installed tool in ~/.local/bin/backplane/.
Each upgrade creates a new versioned directory while keeping all previous versions, leading to significant disk usage growth. For users who frequently update tools, this can result in hundreds of megabytes or even gigabytes of redundant binaries.

For example, after several updates, a user might have:

~/.local/bin/backplane/oc/
  ├── 4.19.5/
  ├── 4.20.8/
  ├── 4.20.9/
  ├── 4.20.10/
  ├── 4.20.11/
  └── 4.21.0/  (currently linked in latest/)

Only the latest version (4.21.0) is actually used, but all previous versions remain on disk.

Solution
This PR introduces a new cleanup subcommand that removes all older versions of installed tools while preserving only the currently active version (the one symlinked in latest/).

Usage:

# Clean up a specific tool
backplane-tools cleanup oc

# Clean up multiple tools
backplane-tools cleanup oc ocm rosa

# Clean up all installed tools
backplane-tools cleanup all
# or simply
backplane-tools cleanup

Testing
Manual testing confirmed that the cleanup command successfully removes older versions while preserving the active version and its symlink.

$ backplane-tools cleanup
Cleaning up the following tools: 

Removing osdctl
Successfully cleaned up osdctl: removed versions: v0.23.2, v0.23.3, v0.23.4, v0.23.5, v0.24.0

Removing backplane-cli
Successfully cleaned up backplane-cli: removed versions: v0.5.7, v0.5.8, v0.5.9, v0.6.0, v0.6.1

Removing rosa
Successfully cleaned up rosa: removed versions: v1.2.40, v1.2.41, v1.2.42, v1.2.43, v1.2.44

Removing ocm-container
Successfully cleaned up ocm-container: removed versions: v2.0.0, v2.0.1, v2.0.2, v2.0.3, v2.0.4

Removing aws
Successfully cleaned up aws: removed versions: 2.13.0, 2.13.5, 2.14.0, 2.14.5, 2.15.0

Removing ocm
Successfully cleaned up ocm: removed versions: v1.0.6, v1.0.7, v1.0.8, v1.0.9, v1.1.0

Removing ocm-addons
Successfully cleaned up ocm-addons: removed versions: v0.8.2, v0.8.3, v0.8.4, v0.8.5, v0.9.0

Removing yq
Successfully cleaned up yq: removed versions: v4.43.2, v4.43.3, v4.43.4, v4.43.5, v4.44.0

Removing gcloud
Successfully cleaned up gcloud: removed versions: 496.0.0, 497.0.0, 498.0.0, 499.0.0, 500.0.0

Removing backplane-tools
Successfully cleaned up backplane-tools: removed versions: v1.0.0, v1.0.1, v1.0.2, v1.0.3, v1.0.4

Removing oc
Successfully cleaned up oc: no old versions found

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This pull-request has been approved by: givaldolins
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