Add field `set_namespace_from_token` to Provider configuration

[vinay-gopalan]

Description

This PR adds a field set_namespace_from_token to the Provider configuration block. This boolean parameter provides an initial escape-hatch to TFVP users who would like to avoid the default behavior in the Provider of setting the namespace from the Auth Login token whenever a Provider-level namespace is not set/specified.

Checklist

• [x] Added CHANGELOG entry (only for user-facing changes)
• [x] Acceptance tests where run against all supported Vault Versions

Output from acceptance testing:

$ make testacc TESTARGS='-run=TestNewProviderMeta'
=== RUN   TestNewProviderMeta
--- PASS: TestNewProviderMeta (0.00s)
=== RUN   TestNewProviderMeta/invalid-nil-ResourceData
=== PAUSE TestNewProviderMeta/invalid-nil-ResourceData
=== CONT  TestNewProviderMeta/invalid-nil-ResourceData
    --- PASS: TestNewProviderMeta/invalid-nil-ResourceData (0.00s)
=== RUN   TestNewProviderMeta/with-provider-ns-only
=== PAUSE TestNewProviderMeta/with-provider-ns-only
=== CONT  TestNewProviderMeta/with-provider-ns-only
    --- PASS: TestNewProviderMeta/with-provider-ns-only (0.01s)
=== RUN   TestNewProviderMeta/with-token-ns-only
=== PAUSE TestNewProviderMeta/with-token-ns-only
=== CONT  TestNewProviderMeta/with-token-ns-only
    --- PASS: TestNewProviderMeta/with-token-ns-only (1.73s)
=== RUN   TestNewProviderMeta/with-provider-ns-and-token-ns
=== PAUSE TestNewProviderMeta/with-provider-ns-and-token-ns
=== CONT  TestNewProviderMeta/with-provider-ns-and-token-ns
    --- PASS: TestNewProviderMeta/with-provider-ns-and-token-ns (0.42s)
=== RUN   TestNewProviderMeta/with-auth-login-and-ns
=== PAUSE TestNewProviderMeta/with-auth-login-and-ns
=== CONT  TestNewProviderMeta/with-auth-login-and-ns
    --- PASS: TestNewProviderMeta/with-auth-login-and-ns (1.72s)
=== RUN   TestNewProviderMeta/with-provider-ns-and-auth-login-with-ns
=== PAUSE TestNewProviderMeta/with-provider-ns-and-auth-login-with-ns
=== CONT  TestNewProviderMeta/with-provider-ns-and-auth-login-with-ns
    --- PASS: TestNewProviderMeta/with-provider-ns-and-auth-login-with-ns (1.97s)
=== RUN   TestNewProviderMeta/set-namespace-from-token-false
=== PAUSE TestNewProviderMeta/set-namespace-from-token-false
=== CONT  TestNewProviderMeta/set-namespace-from-token-false
    --- PASS: TestNewProviderMeta/set-namespace-from-token-false (1.98s)
=== RUN   TestNewProviderMeta/set-namespace-from-token-true
=== PAUSE TestNewProviderMeta/set-namespace-from-token-true
=== CONT  TestNewProviderMeta/set-namespace-from-token-true
    --- PASS: TestNewProviderMeta/set-namespace-from-token-true (2.03s)
PASS