Deprecate datasources and promote the flux_bootstrap_git docs

[phillebaba]

This change deprecates the flux_install and flux_sync datasource. It adds a deprecation notice to the datasources and moves the guides to a deprecated sub category.

Also:

• updates the provider versions in examples and docs use the RC version as per the docs

Prerelease versions are supported (available if explicitly defined but not chosen automatically) with a hyphen (-) delimiter, such as v1.2.3-pre.

• renames the deprecated guides with new alternatives to indicate deprecated version
• fixes the strange file name for new github guide in the registry
  navigation panel by fixing the frontmatter yaml. Because of invalid
  yaml, the renderer was using the file name as the page name in the
  navigation panel. This issue was also being highlighted in the github
  markdown render as:

Error in user YAML: (<unknown>): found a tab character where an
intendation space is expected while scanning a block scalar at line 3 column 14

Based on the docs

If a page_title attribute is not found, the title will default to the filename without the extension.

Part of: #426

[stefanprodan]

I think we should also rename the guides: github.md, gitlab.md and customise.md should contain the updated docs, otherwise Google will point people to old docs.

[phillebaba]

The reason the tests are not passing is because provider dev overrides does not apply to init. Meaning it will annoyingly try to resolve the version of the Flux provider which does not exist.

[stefanprodan]

Is there a fix or should we merge it like this?

[darkowlzz]

Is there a fix or should we merge it like this?

Discussed with @phillebaba about it and decided to remove the version field from the example that's used in the e2e test. All the other examples continue to have the version.
For the record, the alternative of using a local mirror + dev overrides works but that may be future unintended consequences and just removing the version is a simpler workaround for the issue at present.

[stefanprodan]

LGTM

Thanks @phillebaba and @darkowlzz