Enable more rubocop-cops for haml files

In gitlab-foss!21247 (merged) we enable rubocop in haml lint. In order to avoid to much noise, we disabled the following cops. We should decide which ones we want to enable.

Cop	Count (as of 2018)
Cop/LineBreakAfterGuardClauses	22
Cop/LineBreakAroundConditionalBlock !59147 (merged)	0
Cop/ProjectPathHelper	23
GitlabSecurity/PublicSend	6
Layout/LeadingCommentSpace	14
Layout/SpaceAfterColon !58564 (merged)	4
Layout/SpaceAfterComma !58731 (merged)	2
Layout/SpaceAroundOperators	14
Layout/SpaceBeforeBlockBraces	1
Layout/SpaceBeforeComma	6
Layout/SpaceBeforeFirstArg	4
Layout/SpaceInsideArrayLiteralBrackets !59143 (merged)	3
Layout/SpaceInsideHashLiteralBraces	159
Layout/SpaceInsideStringInterpolation	43
Layout/TrailingBlankLines	1073
Lint/BooleanSymbol !59075 (merged)	1
Lint/LiteralInInterpolation	1
Lint/ParenthesesAsGroupedExpression	6
Lint/RedundantWithIndex	1
Lint/Syntax	1
Lint/UselessAssignment	27
Metrics/BlockNesting	3
Naming/VariableName	2
Performance/RedundantMatch	2
Performance/StringReplacement	1
Rails/Presence !17631 (merged) !59600 (merged).	1
Rails/RequestReferer	1
Style/AndOr !59071 (merged)	3
Style/ColonMethodCall	1
Style/ConditionalAssignment	7
Style/HashSyntax	69
Style/IdenticalConditionalBranches	6
Style/NegatedIf	8
Style/NestedTernaryOperator	1
Style/Not !59071 (merged)	1
Style/ParenthesesAroundCondition !59553 (merged)	1
Style/RedundantParentheses !58846 (merged)	19
Style/SelfAssignment	3
Style/Semicolon !59070 (merged)	2
Style/TernaryParentheses	1
Style/TrailingCommaInHashLiteral	2
Style/UnlessElse	3
Style/WordArray	1
Style/ZeroLengthPredicate	6

cc @smcgivern

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The following discussion from gitlab-foss!21247 (merged) should be addressed:

• @reprazent started a discussion: (+2 comments)

  If this is indeed the way to go from review, I'll create an issue for this.

status as of 2021-04

    174  Cop/LineBreakAfterGuardClauses
     21  Cop/ProjectPathHelper
     60  Gitlab/FeatureAvailableUsage
      7  GitlabSecurity/PublicSend
    174  Layout/EmptyLineAfterGuardClause
     10  Layout/LeadingCommentSpace
     20  Layout/SpaceAroundOperators
     17  Layout/SpaceBeforeComma
      1  Layout/SpaceBeforeFirstArg
    243  Layout/SpaceInsideHashLiteralBraces
     35  Layout/SpaceInsideStringInterpolation
   1964  Layout/TrailingEmptyLines
      1  Lint/BooleanSymbol
     16  Lint/LiteralInInterpolation
      2  Lint/ParenthesesAsGroupedExpression
      1  Lint/RedundantWithIndex
      1  Lint/SafeNavigationConsistency
      5  Metrics/BlockNesting
     13  Naming/VariableName
      1  Performance/RedundantMatch
      3  Performance/StringReplacement
    109  Rails/LinkToBlank
      2  Rails/Presence
      2  Rails/RequestReferer
      1  Style/ColonMethodCall
      6  Style/ConditionalAssignment
     74  Style/HashSyntax
      8  Style/IdenticalConditionalBranches
     13  Style/NegatedIf
      2  Style/NestedTernaryOperator
      1  Style/ParenthesesAroundCondition
      6  Style/SelfAssignment
      3  Style/TernaryParentheses
      8  Style/TrailingCommaInHashLiteral
      5  Style/UnlessElse
      8  Style/WordArray
      8  Style/ZeroLengthPredicate