Ignore older updated versions of CTMU after switching to a version with multi-cluster support

[vapopov]

In this PR add fix to ignore existing updated version by v1 client tools managed updates, steps to reproduce:

# Install tsh with v1 CTMU (17.5.4)
$ teleport17.5.4/tsh version
Teleport v17.5.4 git:v17.5.4-0-g0fa760c go1.23.10

# Manually upgrade tsh to v17.6.0 with v2 CTMU, since it is updated by v1 CTMU `~/.tsh/bin/tsh` 
# is going to be created with requested version
$ TELEPORT_TOOLS_VERSION=17.6.0 teleport17.5.4/tsh version
Teleport v17.6.0 git:v17.6.0-0-g4c3b13b go1.23.11
Re-executed from version: 17.5.4

# Upgrade manually installed version of tsh to version 17.7.1
$ teleport17.7.1/tsh version
Teleport v17.6.0 git:v17.6.0-0-g4c3b13b go1.23.11
Re-executed from version: 17.7.1

# A manually upgraded version now always re-executes `~/.tsh/bin/tsh` and logs in to the cluster
# if the required version is the same as the installed version, it is now ignored.
$ teleport17.7.1/tsh login --proxy proxy.example.com
$ teleport17.7.1/tsh version
Teleport v17.6.0 git:v17.6.0-0-g4c3b13b go1.23.11
Re-executed from version: 17.7.1

changelog: Fixed the case where the auto-updated client tools did not use the intended version.

[Tener]

The change itself looks good to me. I think we could make the changelog entry easier to understand, given it is meant to be client-facing. So instead of:

changelog: Fix re-execution of a previously updated version of client tools managed updates for the new version multi-cluster support

Perhaps something like this?

changelog: Fixed the case where the auto-updated client tools did not use the intended version.

[backport-bot-workflows]

@vapopov See the table below for backport results.

Branch	Result
branch/v16	Create PR
branch/v17	Create PR
branch/v18	Create PR