feat: add possibility to customize the User-Agent HTTP header

[bednar]

Closes #370

Proposed Changes

Added possibility to customise the User-Agent HTTP header:

InfluxDBClientOptions options = InfluxDBClientOptions
                .builder()
                .url("http://localhost:8086")
                .clientType("awesome-service")
                .authenticateToken("my-token".toCharArray())
                .build();

=>

User-Agent: influxdb-client-awesome-service/6.3.0

Checklist

• CHANGELOG.md updated
• Rebased/mergeable
• A test has been added if appropriate
• mvn test completes successfully
• Commit messages are conventional
• Sign CLA (if not already signed)

[rhajek]

LGTM. We need also to add clientType settings to our nifi processor