Add support for trustServerCertificate flag

Feature Request

Is your feature request related to a problem? Please describe

In mssql-jdbc library such option is simply available to developer but in r2dbc it needs some struggle (mostly finding out how to enable it) to use SSL with self signed cert.

Describe the solution you’d like

Add new configuration flag which would control trustServerCertificate parameter in underlying mssql-jdbc library. Best to create new parameter in MssqlConnectionConfiguration which would allow using self signed cert.

Describe alternatives you’ve considered

Using generic ConnectionFactoryOptions with adding custom Option but that in fact calls Mssql factory which omits it. After abnalyzing mssql-jdbc driver I found out that in case of using this flag it register dummy trust manager so I mimic that: configBuilder.sslContextBuilderCustomizer(b -> b.trustManager(TrustAllTrustManager.INSTANCE));

Teachability, Documentation, Adoption, Migration Strategy

MssqlConnectionConfiguration.builder().trustServerCertificate();

[thankusWR]

also feel free to review PR https://github.com/r2dbc/r2dbc-mssql/pull/186

[thankusWR]

Great thx, confirmed its ok. The only thing is that I needed to comment out javadocs generation from POM as it was failing:

[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  26.553 s
[INFO] Finished at: 2021-01-28T12:06:04+01:00
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-javadoc-plugin:3.2.0:jar (attach-javadocs) on project r2dbc-mssql: MavenReportException: Error while generating Javadoc: 
[ERROR] Exit code: 1 - warning: unknown enum constant When.MAYBE
[ERROR]   reason: class file for javax.annotation.meta.When not found
[ERROR] javadoc: error - Error fetching URL: https://r2dbc.io/spec/0.9.0.BUILD-SNAPSHOT/api/
[ERROR] javadoc: error - The code being documented uses modules but the packages defined in https://docs.oracle.com/javase/8/docs/api/ are in the unnamed module.
[ERROR] 
[ERROR] Command line was: <localPath>javadoc @options @packages
[ERROR] 
[ERROR] Refer to the generated Javadoc files in '<anotherLocalPath>r2dbc-mssql/target/apidocs' dir.
[ERROR] 
[ERROR] -> [Help 1]
[ERROR] 
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR] 
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException