Feat megalint introduction.

[javydekoning]

Issue #, if available:
#491

Description of changes:
This introduces the first iteration of linters as per #491 and includes some style fixes.

+----MATCHING LINTERS-------+------------------+----------------+------------+
| Descriptor     | Linter   | Criteria         | Matching files | Format/Fix |
+----------------+----------+------------------+----------------+------------+
| CLOUDFORMATION | cfn-lint | .yml|.yaml|.json | 23             | no         |
| DOCKERFILE     | hadolint | Dockerfile       | 1              | no         |
| JAVASCRIPT     | standard | .js              | 1              | no         |
| JSON           | jsonlint | .json            | 9              | no         |
| JSON           | v8r      | .json            | 9              | no         |
| JSON           | prettier | .json            | 9              | no         |
| SPELL          | misspell |                  | 75             | no         |
| TERRAFORM      | tflint   | .tf              | 3              | no         |
| YAML           | yamllint | .yml|.yaml       | 61             | no         |
+----------------+----------+------------------+----------------+------------+

✅ Linted [DOCKERFILE] files with [hadolint] successfully - (0.08s)
- Using [hadolint v2.10.0] https://oxsecurity.github.io/megalinter/latest/v6/descriptors/dockerfile_hadolint
- MegaLinter key: [DOCKERFILE_HADOLINT]
- Rules config: identified by [hadolint]
- Number of files analyzed: [1]

✅ Linted [JSON] files with [jsonlint] successfully - (0.4s)
- Using [jsonlint v11.6.0] https://oxsecurity.github.io/megalinter/latest/v6/descriptors/json_jsonlint
- MegaLinter key: [JSON_JSONLINT]
- Rules config: identified by [jsonlint]
- Number of files analyzed: [9]

✅ Linted [JSON] files with [prettier] successfully - (1.4s)
- Using [prettier v2.7.1] https://oxsecurity.github.io/megalinter/latest/v6/descriptors/json_prettier
- MegaLinter key: [JSON_PRETTIER]
- Rules config: identified by [prettier]
- Number of files analyzed: [9]

✅ Linted [JAVASCRIPT] files with [standard] successfully - (1.97s)
- Using [standard v15.0.1] https://oxsecurity.github.io/megalinter/latest/v6/descriptors/javascript_standard
- MegaLinter key: [JAVASCRIPT_STANDARD]
- Rules config: identified by [standard]
- Number of files analyzed: [1]

✅ Linted [SPELL] files with [misspell] successfully - (0.26s)
- Using [misspell v0.3.4] https://oxsecurity.github.io/megalinter/latest/v6/descriptors/spell_misspell
- MegaLinter key: [SPELL_MISSPELL]
- Rules config: identified by [misspell]
- Number of files analyzed: [75]

✅ Linted [YAML] files with [yamllint] successfully - (1.93s)
- Using [yamllint v1.27.1] https://oxsecurity.github.io/megalinter/latest/v6/descriptors/yaml_yamllint
- MegaLinter key: [YAML_YAMLLINT]
- Rules config: [/.yamllint.yml]
- Number of files analyzed: [61]

✅ Linted [CLOUDFORMATION] files with [cfn-lint] successfully - (6.0s)
- Using [cfn-lint v0.61.5] https://oxsecurity.github.io/megalinter/latest/v6/descriptors/cloudformation_cfn_lint
- MegaLinter key: [CLOUDFORMATION_CFN_LINT]
- Rules config: [.cfnlintrc.yml]
- Number of files analyzed: [23]

✅ Linted [TERRAFORM] files with [tflint] successfully - (13.07s)
- Using [tflint v0.35.0] https://oxsecurity.github.io/megalinter/latest/v6/descriptors/terraform_tflint
- MegaLinter key: [TERRAFORM_TFLINT]
- Rules config: [.tflint.hcl]
- Number of files analyzed: [3]
[Pre][TERRAFORM_TFLINT] run: [tflint --init --config /action/lib/.automation/.tflint.hcl] in cwd [/]
[Pre][TERRAFORM_TFLINT] Installing `aws` plugin...
Installed `aws` (source: github.com/terraform-linters/tflint-ruleset-aws, version: 0.13.3)


✅ Linted [JSON] files with [v8r] successfully - (25.56s)
- Using [v8r v0.13.0] https://oxsecurity.github.io/megalinter/latest/v6/descriptors/json_v8r
- MegaLinter key: [JSON_V8R]
- Rules config: identified by [v8r]
- Number of files analyzed: [9]


+----SUMMARY--------+----------+---------------+-------+-------+--------+--------------+
| Descriptor        | Linter   | Mode          | Files | Fixed | Errors | Elapsed time |
+-------------------+----------+---------------+-------+-------+--------+--------------+
| ✅ CLOUDFORMATION | cfn-lint | list_of_files |    23 |       |      0 |         6.0s |
| ✅ DOCKERFILE     | hadolint | file          |     1 |       |      0 |        0.08s |
| ✅ JAVASCRIPT     | standard | list_of_files |     1 |       |      0 |        1.97s |
| ✅ JSON           | jsonlint | list_of_files |     9 |       |      0 |         0.4s |
| ✅ JSON           | prettier | list_of_files |     9 |       |      0 |         1.4s |
| ✅ JSON           | v8r      | list_of_files |     9 |       |      0 |       25.56s |
| ✅ SPELL          | misspell | list_of_files |    75 |       |      0 |        0.26s |
| ✅ TERRAFORM      | tflint   | file          |     3 |       |      0 |       13.07s |
| ✅ YAML           | yamllint | list_of_files |    61 |       |      0 |        1.93s |
+-------------------+----------+---------------+-------+-------+--------+--------------+

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[sbkok]

Thanks for contributing this.
I've added a few comments, some that need discussion, happy to jump in a call if needed.

[javydekoning]

@sbkok this is complete and ready for another review.

[sbkok]

Looks great! Thanks for adding those instructions in the docs and updating the build status images too!