Add key action for + to do kubectl apply -f

[yeahdongcn]

k9s is such a great tool for my daily work. The only problem is I have to switch to a different terminal tab or window if I want to apply new YAML files.
This PR added key action for + to do kubectl apply -f. The process can be described as follows.

1. Copy YAML file content from your browser or somewhere else
2. Press + (shift + =) to open a temp file
3. Paste it then save and quit
4. kubectl apply -f

[yeahdongcn]

Maybe a cure for #1323?

[derailed]

@yeahdongcn Thank you for this PR. Do you know the dir command provides for listing and applying manifests?

[yeahdongcn]

Oh, I didn't realize there was a similar command already implemented. dir looks awesome! But this PR actually tries to fulfill another user scenario that one can use an online manifest w/o creating a local file.

[derailed]

@yeahdongcn Thank you for the clarification! Good point. Looks like we have some conflicts. Could you update?

[yeahdongcn]

@yeahdongcn Thank you for the clarification! Good point. Looks like we have some conflicts. Could you update?

@derailed Done. Please see the latest commit. Thanks.

[ryaminal]

learned about :dir . from this PR, super helpful

also, this PR is super exciting to see for such an amazing tool.

[yeahdongcn]

@derailed It's been quite some time... Could you get this merged?

[mih-kopylov]

@derailed I'm looking for this feature for quite a while. Could you please facilitate to get this PR merged?

[yeahdongcn]

Code rebased from upstream/main.