…vider (#1730)

This PR allows the Java auth lib to provide either an X509 mTLS provider or SecureConnect mTLS provider based on availability and under a common "MtlsProvider" interface. The Java GAX lib will be refactored to use this factory and interface in a subsequent PR.

…1765)

Changed "preferrable" to "preferable" in a comment within the getRequestMetadata method.

* Fix duplicate "the" in Javadoc comments

Removes occurrences of "the the" in Javadoc comments in the following files:
- oauth2_http/java/com/google/auth/oauth2/OAuth2Credentials.java
- oauth2_http/java/com/google/auth/oauth2/ServiceAccountJwtAccessCredentials.java
- oauth2_http/java/com/google/auth/oauth2/JwtCredentials.java

* fix format

The Javadoc for ExternalAccountCredentials.java incorrectly referred to
`GoogleCredential.Builder`. This commit corrects the reference to
`GoogleCredentials.Builder`.

ServiceAccountCredentials.java repeatedly referred to "Oauth Endpoint"
instead of "OAuth Endpoint" in comments. This commit corrects these
misspellings.

Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>

I corrected improper capitalization of "GitHub" in documentation and workflow files.

Changes were made in:
- .github/workflows/ci.yaml
- RELEASE.md
- .kokoro/build.bat

Removes extra spaces after the '###' marker in the 'Workforce Identity Federation' heading in README.md.

Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>