Env config - make profile optional

[THardy98]

What was changed

The profile parameter is now optional, instead of defaulting to a value of default.

Why?

A defined profile value is an explicit request for a specific profile in a provided configuration. Providing a default value made it impossible for a user to provide zero configuration (they would have to define a default profile in their TOML).

However, we want to allow users to provide zero configuration and have it default to localhost:7233 address and default namespace.

This change makes that possible in combination with temporalio/sdk-rust#968

2. How was this tested:
   Existing integration tests

3. Any docs updates needed?
   This change achieves parity with the docs

[THardy98]

Marking as draft until temporalio/sdk-rust#968 is merged (will update core submodule after). This gives us default values for address and namespace

[THardy98]

Marking as draft until temporalio/sdk-core#968 is merged (will update core submodule after). This gives us default values for address and namespace

No longer blocked (core PR closed).