feat: update to Grails 7.0.0-M5 and setup project for forward compatibility

[jdaugherty]

Are one of you (@sbglasius @jamesfredley @matrei ) available to review these changes? I updated the plugin so that it uses the dependencies-starter-web/test since it's a grails plugin and these are "provided". I updated the test project to explicitly use M5 (to show that grails snapshot is currently forward compatible)

The generated pom after these changes:

    <?xml version="1.0" encoding="UTF-8"?>
    <project xmlns="http://maven.apache.org/POM/4.0.0" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
      <!-- This module was also published with a richer model, Gradle metadata,  -->
      <!-- which should be used instead. Do not delete the following line which  -->
      <!-- is to indicate to Gradle or any Gradle module metadata file consumer  -->
      <!-- that they should prefer consuming it instead. -->
      <!-- do_not_remove: published-with-gradle-metadata -->
      <modelVersion>4.0.0</modelVersion>
      <groupId>org.grails.plugins</groupId>
      <artifactId>grails-mail</artifactId>
      <version>5.0.1-SNAPSHOT</version>
      <dependencies>
        <dependency>
          <groupId>jakarta.mail</groupId>
          <artifactId>jakarta.mail-api</artifactId>
          <scope>compile</scope>
          <version>2.1.3</version>
        </dependency>
        <dependency>
          <groupId>org.eclipse.angus</groupId>
          <artifactId>jakarta.mail</artifactId>
          <version>2.0.3</version>
          <scope>runtime</scope>
        </dependency>
      </dependencies>
      <name>Grails Mail Plugin</name>
      <description>Provides Mail support to a running Grails application</description>
      <url>https://github.com/grails-plugins/grails-mail</url>
      <licenses>
        <license>
          <name>The Apache Software License, Version 2.0</name>
          <url>https://www.apache.org/licenses/LICENSE-2.0.txt</url>
          <distribution>repo</distribution>
        </license>
      </licenses>
      <scm>
        <url>https://github.com/grails-plugins/grails-mail</url>
        <connection>scm:git@github.com:grails-plugins/grails-mail.git</connection>
        <developerConnection>scm:git@github.com:grails-plugins/grails-mail.git</developerConnection>
      </scm>
      <issueManagement>
        <system>GitHub Issues</system>
        <url>https://github.com/grails-plugins/grails-mail/issues</url>
      </issueManagement>
      <developers>
        <developer>
          <id>candrews</id>
          <name>Craig Andrews</name>
        </developer>
        <developer>
          <id>ldaley</id>
          <name>Luke Daley</name>
        </developer>
        <developer>
          <id>pledbrook</id>
          <name>Peter Ledbrook</name>
        </developer>
        <developer>
          <id>jeffscottbrown</id>
          <name>Jeff Brown</name>
        </developer>
        <developer>
          <id>graemerocher</id>
          <name>Graeme Rocher</name>
        </developer>
        <developer>
          <id>marcpalmer</id>
          <name>Marc Palmer</name>
        </developer>
        <developer>
          <id>sbglasius</id>
          <name>Søren Berg Glasius</name>
        </developer>
        <developer>
          <id>matrei</id>
          <name>Mattias Reichel</name>
        </developer>
      </developers>
    </project>