BFD-3923: Use versions in child module references

[mjburling]

JIRA Ticket:
BFD-3923

What Does This PR Do?

This pins the bfd-terraservice module to a known, good version at tagged release 2.181.0 so that we can innovate on the child module for forthcoming fargate and greenfield migrations, without any concerns toward introducing errors.

What Should Reviewers Watch For?

If you're reviewing this PR, please check for these things in particular:

• Reviewers should be familiar with various modules in terraform, especially the so-called Root Modules and Child Modules; for our purposes, the terraservices themselves, i.e. base, common, eft and so on are root modules, while the bfd-terraservice module is a child module. This PR seeks to reference that bfd-terraservice by a tag reference.
• Reviewers may note that while this feature isn't particularly well-documented in my opinion, referencing a module that isn't at the root of a given source is possible via what Hashicorp calls Modules in Package Sub-directories

What Security Implications Does This PR Have?

Please indicate if this PR does any of the following:

• Adds any new software dependencies

• Modifies any security controls

• Adds new transmission or storage of data

• Any other changes that could possibly affect security?

• I have considered the above security implications as it relates to this PR. (If one or more of the above apply, it cannot be merged without the ISSO or team security engineer's (@sb-benohe) approval.)

• I have created tests to sufficiently ensure the reliability of my code, if applicable. If this is a modification to an existing piece of code, I have audited the associated tests to ensure everything works as expected.

Validation

Have you fully verified and tested these changes? Is the acceptance criteria met? Please provide reproducible testing instructions, code snippets, or screenshots as applicable.

This no-op change was evaluated against all terraservices in test–executing e.g. terraform init && terraform apply didn't yield any meaningful diffs.