docs: create pre/post-deploy getting started

[StackScribe]

Replaces #1337, #1336, and other corrupted PRs.

Satisfies #1302

Getting started guide for the orchestrate pre/post-deployment checks use case, based on Andi's demo video

Comments welcome but this still needs some writing

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[agardnerIT]

@aepfli markdown checks seem to be failing (from what I interpret) because /docs/readme.md contains a link to localhost.

1. This PR doesn't touch docs/readme.md - is there a way for MDLint to only run on changed files during PRs? This might speed up checks too.
2. The link to localhost in docs/readme is actually necessary and thus valid. Can we ignore that file + link combination in MDLint?

[aepfli]

1. This PR doesn't touch [docs/readme.md ](https://github.com/keptn/lifecycle-toolkit/blob/main/docs/README.md)- is there a way for MDLint to only run on changed files during PRs? This might speed up checks too.

The checks only needs one minute, and most of the time it is actually the setup rather than the test itself, i do not see a lot of benefit in improving this. the investments vs the gain will be little

2. The link to localhost in `docs/readme` is actually necessary and thus valid. Can we ignore that file + link combination in MDLint?

the markdown link check fails due to:

 ERROR: 1 dead links found!
[✖] ../../implementing/integrate.md → Status: 400

in: FILE: docs/content/en/docs/getting-started/observability/_index.md

There is a bad markdown link within the file referencing another. localhost already has an exception as seen here

lifecycle-toolkit/.github/mlc_config.json

Lines 2 to 9 in 2c51231

	"ignorePatterns": [
	{
	"pattern": "^http://localhost"
	},
	{
	"pattern": "^/images/why-keptn"
	}
	],

[aepfli]

Rebased and fixed issues, pr is green.

Additional note regarding running changes only for the files changed. Especially a link checker is a good example for such a test because we also want to check the "incoming" links from other readmes. Detecting if an internal link changed, or a file is suddenly not available anymore etc. is not such a trivial topic.

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[thisthat]

Follow-ups can be tackle in #1444