ENH: pkg mirror, static xar configs

[ZLLentz]

Description

Main changes:

• Optionally/default configure PLCs to load their packages from an internal pcds mirror of Beckhoff's repositories
• Allow you to specify a static TwinCAT runtime (XAR) version in your config, rather than whichever random version your PLC started with (or in some cases, whichever was most recent online at time of setup). This required the internal mirror to implement.
• The XAR defaults to 4026.3.55 because it's what I've been testing with, but is defined statically in each host's vars file instead of in the group vars files. This prevents us from accidentally updating any XARs automatically.
• Allow us to enable/disable the FreeBSD, TCBSD, and SLAC package repositories independently and reversibly.

Smaller changes:

• make the psproxy and psntp configs reversible
• new default: no psproxy pkg config (not needed with the internal mirror)
• Remove plc-tmo-tmp-vac, it's been renamed and will need a full re-boostrapping later.
• Fix a small typo on the ecs-user's bash shell path. I had fixed this previously but it must have not been properly committed.

Motivation and Context

• The TCBSD repos only provide the very most recent version of TwinCAT packages, such as the XAR.
• In order to support static configs over time, the simplest solution is to mirror the builds locally and stamp them with the XAR version numbers.
• These packages are being hosted out of the same servers that provide files for the rhel7/rocky9 servers because sharing infrastructure is great.
• My long learning doc: https://confluence.slac.stanford.edu/display/PCDS/TcBSD+Local+pkg+Server
• IT helped me with the file server stuff: https://jira.slac.stanford.edu/browse/ECS-4795

How Has This Been Tested?

Interactively on PLCs that run BSD13 and BSD14

Where Has This Been Documented?

Added the steps to https://confluence.slac.stanford.edu/display/PCDS/TcBSD+Ansible+Workflows
Looking for other places to make relevant callouts

Pre-merge checklist

• Code works interactively
• Code works interactively in dry_run mode
• Code contains descriptive docstrings, including context and API
• Pre-commit passes on GitHub Actions
• Documentation under https://confluence.slac.stanford.edu/display/PCDS/TcBSD has been updated appropriately

[ZLLentz]

It'd be neat if this made it in before Divya tried out the scripts tomorrow, but it isn't fully necessary. If not merged by EOD, then I'm going to cherrypick the small bugfix with the bash path into a separate PR and deploy just that change.

[slactjohnson]

I don't know enough about ansible or BSD (yet) to comment to evaluate the playbooks for accuracy, but I don't see anything that stands out as incorrect. All the steps makes sense to me as things that should be done.