BAO_ADDR is not propagated to the token helper when provided as -address

[ruuda]

Describe the bug

The token helper might inherit BAO_ADDR from the environment, but if the address is configured through the -address flag instead, then the token helper has no way of knowing about the address.

To Reproduce
Steps to reproduce the behavior:

1. Set a program that prints BAO_ADDR and then fails as the token helper in ~/.bao.
2. Run BAO_ADDR=foo bao login, observe it gets the BAO_ADDR.
3. Run bao login -address foo, observe it does not get BAO_ADDR.

Expected behavior
The token helper needs to know the address of the instance it’s connecting to, so it can store a token per instance, that is the point of the token helper. Therefore, bao needs to set BAO_ADDR in the environment of the token helper it executes, and not rely on it being present implicitly.

Environment:

• OpenBao Server Version (retrieve with bao status): irrelevant
• OpenBao CLI Version (retrieve with bao version): OpenBao v2.0.0-alpha20240329 ('74c2dddb0612b9a3da79384c20638266aa7de407'), built 2024-04-26T10:19:19Z
• Server Operating System/Architecture: Linux 6.8.7 / x86-64

OpenBao server configuration file(s): irrelevant

Additional context

This bug report is an adaptation of hashicorp/vault#22257.

[ruuda]

I implemented a fix for this in hashicorp/vault#23218 that I want to port to OpenBao. The pull request was never included into Hashicorp Vault, so the Source-Available License Policy should not be a problem.

The changes touch parts of the code that would conflict with #313, so before I go ahead and adapt that change for OpenBao, I’m waiting to see what happens to #313.