docs: add provider section with examples

[salasberryfin]

Description

This change restructures the providers section under Reference Guides which now contains, apart from the table with supported providers, provisioning examples for the most important providers: CAPA and Kubeadm+CAPD. This is added to the Getting Started example based on CAPRKE2+CAPD.

These two new examples include pre-configured sample templates so users can test CAPI provisioning with a basic cluster deployment.

Addresses some of the requirements from #117. Documenting RKE2+EC2 is still pending.

[alexander-demicev]

Looks good, can you remove "fixes # 81"? We will need to add RKE2+EC2 based later when CAPA release is done #117.

[salasberryfin]

Thanks @alexander-demicev. Rebased PR and addressed suggestions.

[salasberryfin]

Thanks for the review @yiannistri. The PR is now updated and ready to be reviewed again.

[salasberryfin]

Thanks @furkatgofurov7 @yiannistri. I merged CAPI Providers guides into a single page and used tabs for some steps while keeping the common parts (like cluster/namespace import).

[furkatgofurov7]

Thanks @salasberryfin LGTM, one small suggestion

[yiannistri]

Nice work @salasberryfin 👍 Just one tiny suggestion to keep things consistent.

[yiannistri]

Suggested change

	2. View **cluster1.yaml** to ensure there are no tokens. You can make any changes you want as well.
	2. View **cluster1.yaml** to ensure there are no tokens (i.e. SSH keys or cloud credentials). You can make any changes you want as well.

Mostly for consistency reasons, although it's fairly unlikely for the Docker provider.

[furkatgofurov7]

@yiannistri you should not need those for docker provider