Add a list_all_columns function to store and handler

[rom1504]

What changes are proposed in this pull request?

Add a list_all_columns function to store and handler
it takes as argument a list of experiment id
it returns the metrics, tags, params and attributes names
present for these experiments

this is particularly useful in an UI proposing to choose
columns

How is this patch tested?

• test in sql alchemy store
• test in file store
• test in handler

Release Notes

Is this a user-facing change?

• No. You can skip the rest of this section.
• Yes. Give a description of this change to be included in the release notes for MLflow users.

add list_all_columns in API

What component(s) does this PR affect?

• UI
• CLI
• API
• REST-API
• Examples
• Docs
• Tracking
• Projects
• Artifacts
• Models
• Scoring
• Serving
• R
• Java
• Python

How should the PR be classified in the release notes? Choose one:

• rn/breaking-change - The PR will be mentioned in the "Breaking Changes" section
• rn/none - No description will be included. The PR will be mentioned only by the PR number in the "Small Bugfixes and Documentation Updates" section
• rn/feature - A new user-facing feature worth mentioning in the release notes
• rn/bug-fix - A user-facing bug fix worth mentioning in the release notes
• rn/documentation - A user-facing documentation change worth mentioning in the release notes

[codecov-io]

Codecov Report

Merging #46 into add_total_count will not change coverage.
The diff coverage is n/a.

@@               Coverage Diff                @@
##           add_total_count      #46   +/-   ##
================================================
  Coverage            83.46%   83.46%           
================================================
  Files                   20       20           
  Lines                 1010     1010           
================================================
  Hits                   843      843           
  Misses                 167      167

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[t-henri]

You shouldn't use the POST method for this endpoint, IMO it should only be a GET

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.46%. Comparing base (6fb9443) to head (82bb9d1).
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Additional details and impacted files

@@               Coverage Diff                @@
##           add_total_count      #46   +/-   ##
================================================
  Coverage            83.46%   83.46%           
================================================
  Files                   20       20           
  Lines                 1010     1010           
================================================
  Hits                   843      843           
  Misses                 167      167           

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