Add support for ldap client_tls settings

[JanMa]

This adds support for the client_tls_cert and client_tls_key
settings in the vault_ldap_auth_backend resource.

Community Note

• Please vote on this pull request by adding a 👍 reaction to the original pull request comment to help the community and maintainers prioritize this request
• Please do not leave "+1" comments, they generate extra noise for pull request followers and do not help prioritize the request

Release note for CHANGELOG:

`resource/vault_ldap_auth_backend`: Add `client_tls_cert` and `client_tls_key` options

Output from acceptance testing:

$ make testacc TESTARGS='-run=TestLDAPAuthBackend_tls'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test $(go list ./... |grep -v 'vendor') -v -run=TestLDAPAuthBackend_tls -timeout 120m
?       github.com/hashicorp/terraform-provider-vault   [no test files]
?       github.com/hashicorp/terraform-provider-vault/cmd/coverage      [no test files]
?       github.com/hashicorp/terraform-provider-vault/cmd/generate      [no test files]
testing: warning: no tests to run
PASS
ok      github.com/hashicorp/terraform-provider-vault/codegen   (cached) [no tests to run]
?       github.com/hashicorp/terraform-provider-vault/generated [no test files]
WARNING: Package "github.com/golang/protobuf/protoc-gen-go/generator" is deprecated.
        A future release of golang/protobuf will delete this package,
        which has long been excluded from the compatibility promise.

testing: warning: no tests to run
PASS
ok      github.com/hashicorp/terraform-provider-vault/generated/datasources/transform/decode    (cached) [no tests to run]
WARNING: Package "github.com/golang/protobuf/protoc-gen-go/generator" is deprecated.
        A future release of golang/protobuf will delete this package,
        which has long been excluded from the compatibility promise.

testing: warning: no tests to run
PASS
ok      github.com/hashicorp/terraform-provider-vault/generated/datasources/transform/encode    (cached) [no tests to run]
WARNING: Package "github.com/golang/protobuf/protoc-gen-go/generator" is deprecated.
        A future release of golang/protobuf will delete this package,
        which has long been excluded from the compatibility promise.

testing: warning: no tests to run
PASS
ok      github.com/hashicorp/terraform-provider-vault/generated/resources/transform/alphabet    (cached) [no tests to run]
WARNING: Package "github.com/golang/protobuf/protoc-gen-go/generator" is deprecated.
        A future release of golang/protobuf will delete this package,
        which has long been excluded from the compatibility promise.

testing: warning: no tests to run
PASS
ok      github.com/hashicorp/terraform-provider-vault/generated/resources/transform/role        (cached) [no tests to run]
WARNING: Package "github.com/golang/protobuf/protoc-gen-go/generator" is deprecated.
        A future release of golang/protobuf will delete this package,
        which has long been excluded from the compatibility promise.

testing: warning: no tests to run
PASS
ok      github.com/hashicorp/terraform-provider-vault/generated/resources/transform/template    (cached) [no tests to run]
WARNING: Package "github.com/golang/protobuf/protoc-gen-go/generator" is deprecated.
        A future release of golang/protobuf will delete this package,
        which has long been excluded from the compatibility promise.

testing: warning: no tests to run
PASS
ok      github.com/hashicorp/terraform-provider-vault/generated/resources/transform/transformation      (cached) [no tests to run]
?       github.com/hashicorp/terraform-provider-vault/schema    [no test files]
testing: warning: no tests to run
PASS
ok      github.com/hashicorp/terraform-provider-vault/util      (cached) [no tests to run]
WARNING: Package "github.com/golang/protobuf/protoc-gen-go/generator" is deprecated.
        A future release of golang/protobuf will delete this package,
        which has long been excluded from the compatibility promise.

=== RUN   TestLDAPAuthBackend_tls
--- PASS: TestLDAPAuthBackend_tls (0.41s)
PASS
ok      github.com/hashicorp/terraform-provider-vault/vault     (cached)
...

[jasonodonnell]

LGTM, thanks!