[improve][client] Implement tls_client_auth for OAuth2

[izumo27]

Motivation

Currently, ClientCredentialsFlow of AuthOauth2 supports only client_secret_post.
This PR adds tls_client_auth.
cf. apache/pulsar#25538

Modifications

• Add clientId, tlsCertFile, tlsKeyFile, and trustCertsFilePath params.
  • tlsCertFile and tlsKeyFile params are required for tls_client_auth.

Verifying this change

• Make sure that the change passes the CI checks.
  • [improve][client] Implement tls_client_auth for OAuth2 izumo27/pulsar-client-go#1

This change added tests and can be verified as follows:

• Added tests for tls_client_auth

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API: no
• The schema: no
• The default values of configurations: no
• The wire protocol: no

Documentation

• Does this pull request introduce a new feature? yes
• If yes, how is the feature documented? GoDocs