feat(js/plugins/vertexai): add support to anthropic prompt caching

[amondnet]

Description here... Help the reviewer by:

• close #2885

When using Anthropic models, you can set up cache control for system messages. You can enable this feature by adding a cacheControl property to the custom field of a message. The only currently supported cache type is ephemeral.

For example, to use cache control for a specific system message, you would set it up like this:

const llmResponse = await ai.generate({
  model: claude3Sonnet, // or another Anthropic model
  messages: [
    {
      role: 'system',
      content: [
        {
          text: 'This is an important instruction that can be cached.',
          custom: {
            cacheControl: {
              type: 'ephemeral',
            },
          },
        },
      ],
    },
    {
      role: 'user',
      content: [{ text: 'What should I do when I visit Melbourne?' }],
    },
  ],
});

---

https://github.com/anthropics/anthropic-sdk-typescript/releases/tag/sdk-v0.33.0 https://github.com/anthropics/anthropic-sdk-typescript/pull/631

Checklist (if applicable):

• [x] PR title is following https://www.conventionalcommits.org/en/v1.0.0/
• [x] Tested (manually, unit tested, etc.)
• [x] Docs updated (updated docs or a docs bug required)