Add __meta_ec2_region and __meta_lightsail_region SD meta labels

[candlerb]

Fixes #11320

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@juliusv:
I don't know whether model.LabelValue with an empty string is valid. However, as far as I can see, d.cfg.Region can never be empty string anyway (if it were, the AWS API client would return an error). Hence I haven't checked for this condition.

I have tested this with EC2 only. I don't use Lightsail, but I've made the corresponding change for that too for consistency.

I have not put anything in CHANGELOG, I don't know which branch this will end up being applied to.

[juliusv]

Ah great, thanks for including Lightsail as well. Yes, I think d.cfg.Region should always be set, and even if it wasn't, labels with empty values are discarded upon ingestion, so it shouldn't hurt much if we are wrong about that.

main is the right branch 👍

[juliusv]

(oh and I allowed myself to change the title of the PR to include the other label as well, so that whoever writes the changelog entries for the next release doesn't miss Lightsail)

[candlerb]

BTW I didn't know where else to report this, but these two lines are crossed-over in the release notes for Pre-release v2.39.0-rc.0 - 2.39.0-rc.0 / 2022-09-27:

[ENHANCEMENT] AWS Lightsail SD: Add __meta_ec2_region label. #11326
[ENHANCEMENT] AWS EC2 SD: Add ____meta_lightsail_region label. #11326

It should say:

[ENHANCEMENT] AWS EC2 SD: Add __meta_ec2_region label. #11326
[ENHANCEMENT] AWS Lightsail SD: Add ____meta_lightsail_region label. #11326

[juliusv]

@candlerb Ah thanks for flagging that! That was done in #11344. I sent a PR to fix it in #11377.