Add card feature to msteamsv2_config

[jverger]

The goal of this PR is to add an option card to the msteamsv2_config configuration.

If this card option is not used, the default behaviour is keept using title and text values.

Here is an example screenshot of the default result in msteams channel:

When using card option, the user is able to customize the msteams card rendering output by using a custom template file and configuring card option to use this template.

Here is an example screenshot of the output result in msteams channel when using card option:

To be honest, it's the first time i'm developing in go and create a PR.
Hope it will be not so bad :)

[jverger]

All checks have passed 🎉 , waiting for someone to merge this PR ⌚

[grobinson-grafana]

I would really like to avoid pushing users towards templating JSON blobs. It has a lot of problems that I've explained in a couple other PRs such as #3799 (comment).

I think supporting cards would be excellent, because visually its a massive improvement, but just not with templated JSON.

[jverger]

Nevermind, I would have try.
Thank you for your answer.