[SPIKE][download-requirements] Add manifest handling for downloading only needed data

[sbbroot]

Is your spike related to a problem or idea? Please describe.
By default download-requirements should download all the data defined in the requirements files.
If manifest file is provided for the download-requirements script, it should parse it and choose the only needed data for target cluster.

Describe the outcome you'd like
Separate issues should be created for implementing:

• handling the manifest file
• dashboards download
• files download
• images download
• packages download
  With full description on how to implement the solution

What is the reason or source for the spike
This is a long wanted feature for the download-requirements script to work much faster.

Additional context

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DoD checklist

• Reader is able to understand the results of spike
• The results of the spike are presented in a table (to show simply what are compared or researched parameters) / not applicable
• Each value / cell in the results table is described more deeply below
• Demo of the spike (automated as much as possible)
• Design doc updated

[sbbroot]

Separate SPIKE was added for the packages (#3094)

[sbbroot]

Issue regarding the manifest was created (#3097)

[sbbroot]

images - (#3106)
files - (#3116)

[sbbroot]

dashboards - no need for optimization since downloading all of them takes roughly 2 - 5 seconds:

[to-bar]

dashboards - no need for optimization since downloading all of them takes roughly 2 - 5 seconds

I would opt for adding the adaptive functionality also for dashboards but in this case not because of speed but for scenario when a dashboard's URL is broken and user doesn't want to deploy Grafana. Having adaptive mode for dashboards would allow to deploy a cluster successfully despite the broken link(s).

[sbbroot]

I agree that dashboards should not be downloaded when Grafana is not on a list of components that will be used. As for URLs there is a separate issue on adding alternative URLs.

[sbbroot]

Added issue for Grafana dashboards: (#3131).