feat: Enhance Maven plugin with new actions and utilities

[glaulher]

This pull request introduces several enhancements and new functionalities to the Maven plugin, improving its usability and extending its capabilities. The following changes have been made:

New Features:

add_dependency_to_pom.lua: Added functionality to facilitate the addition of dependencies directly to the pom.xml file, streamlining the process for users. create_project.lua: Introduced a new action to create Maven projects more efficiently, providing a user-friendly experience. init.lua: Included initialization routines for the new action scripts, ensuring proper setup and integration. create_floating_window.lua: Added utility to create floating windows for user inputs, enhancing the plugin's interface. open_maven_central.lua: Implemented a utility function to open Maven Central, allowing users to easily access repositories and dependencies. validate.lua: Created a validation module to check configurations and ensure correct setup. Modifications:

commands.lua: Updated command definitions to incorporate the new functionalities, making it easier for users to execute Maven-related tasks. config.lua: Modified configuration settings to include a new field for specifying the Maven Central URL, allowing for customization. init.lua: Adjusted initialization logic to accommodate the new utilities and actions, improving overall plugin performance.

if you want to test before merging:

 {
    'glaulher/maven.nvim',
    branch = 'newfeat',
    cmd = { 'Maven', 'MavenExec' },
    dependencies = 'nvim-lua/plenary.nvim',
    config = function()
      require('maven').setup {
        executable = 'mvn',
        -- maven_central_url = 'https://mvnrepository.com/repos/central', if nil https://central.sonatype.com/
      }
    end,
  },