Add fluent-bit chart

[torstenwalter]

This adds the fluent-bit chart from the loki repository to this repo.

It includes the existing history. You can verify it yourself by checking the history for individual files as in the example:

$ git log --oneline charts/fluent-bit/Chart.yaml
58aec3e helm chart: Fix broken logo (#2651)
0cd01e9 Update helm and jsonnet to new release (#2809)
365de55 K8S-Logging.Exclude &  and Mem_Buf_Limit toggle (#2746)
51a57d2 Promtail: (and also fluent-bit) change the max batch size to 1MB  (#2710)
03b944e updating images to 1.6.0 (#2504)
51cb8a9 Add optional secret to pull Docker image in fluent-bit chart (#2489)
da9a22d Add projected and downwardAPI volume types to PodSecurityPolicy (#2355) (#2366)
ca6f2e0 helm: add annotations to service monitor (#2258)
8a35174 Allow configuring more options for output configuration (#2089)
e864f1e updating all the images to 1.5.0 release (#2100)
4909736 Add extraOutputs variable to support multiple outputs for fluent-bit (#2040)
98d95fa Fix fluent-bit metrics (#1915)
79234cb updating helm and ksonnet to 1.4.1 updating Fluent Bit to correct image
6411263 helm : fix fluent-bit parser configuration syntax (#1534)
f4e1e78 helm: add podsecuritypolicy for fluent-bit (#1506)
e70549b Allow to define custom parsers to use with fluentbit.io/parser annotation (#1430)
92f3a94 Helm: Fix the reference error of loki/loki helm chart (#1056)
d774d0a rollback fluent-bit push path until we release 0.4
1a7a35e fluent-bit shared object go plugin (#847)

Filtering the history was did a great trick on reducing the history size.

In addition to migrating the repositories the following things have been done:

• all linting errors in Markdown files have been resolved
• minor version of the charts has been increased
  The goal of this is to publish a newer version of the charts from this repo. I choose to increase the minor version so that it's possible to increase the patch version to deprecate the existing charts and point to the new location.
• READMEs was adjusted to take the new helm repository location into account.

Note:

• I disabled validation of maintainers as "Loki Maintainers" is not a valid GitHub username.
  Here one should decide if one explicitly want's to name all maintainers or refer to a github team which exists.
  Not sure if GitHub teams could be resolved, but we could at least use it in CODEOWNERS file.
• DCO check is failing as history was imported. We should ignore it for this PR.

Part-of: grafana/loki#2593

[slim-bean]

LGTM!