Update documenation for retrieving a list of all templates (dynamic & legacy)

[thinkingserious]

Issue Summary

Please update the USAGE.md and corresponding \example with the call to list all templates.

This is the API call required: GET https://api.sendgrid.com/v3/templates?generations=legacy,dynamic

Acceptance Criteria

• The Usage.md file demonstrates how to use this API call to retrieve all templates: GET https://api.sendgrid.com/v3/templates?generations=legacy,dynamic
• The corresponding /example file demonstrates how to use this API call to retrieve all templates: GET https://api.sendgrid.com/v3/templates?generations=legacy,dynamic

[thinkingserious]

Specifically these locations:
https://github.com/sendgrid/sendgrid-java/blob/master/USAGE.md#get-templates
https://github.com/sendgrid/sendgrid-java/tree/master/examples/templates

Thanks!

[svachmic]

What is the status on using templates now? Both links on usage lead to legacy templates. Which templates are we supposed to be using now?

[svachmic]

@childish-sambino why is this issue closed when it still hasn't been resolved? Everything is still legacy, nothing points to the new URLs, e.g. this one:

https://sendgrid.com/docs/ui/sending-email/how-to-send-an-email-with-dynamic-transactional-templates/

Or is this to be understood as ALL templates are now marked as legacy and we should look for a different solution as it won't be supported anymore? Thanks!

[childish-sambino]

This issue is for updating the examples for retrieving all templates (default is legacy-only). This was fixed by #504

Transactional/dynamic template docs are already in the usage guide: https://github.com/sendgrid/sendgrid-java/blob/main/USE_CASES.md#transactional-templates

[svachmic]

@childish-sambino this sentence with a link:

For this example, we assume you have created a transactional template in the UI or via the API. Following is the template content we used for testing.

Is exactly the one I reported in the message above - the link under the transactional template leads to legacy documentation and not the most recent one.

[childish-sambino]

Updated: b7de4b6