Slack-sdk

The version is available as a pre-release on PyPI: https://pypi.org/project/slackclient/2.6.0rc1/
Refer to [v2.6.0 milestone](https://github.com/slackapi/python-slackclient/milestone/5) to know the complete list of the issues resolved by this release.

**New Features**

1. [Block Kit] 659 Add complete supports for Block Kit components and fixed a few existing bugs as well (500 519 623 632 635 639 676) - Thanks seratch diurnalist ruberVulpes jeremyschulman e271828- RodneyU215
2. [Signature] 686 Add slack.signature.SignatureVerifier for request verification - Thanks seratch
3. [WebClient] 682 Add missing Grid admin APIs (`admin.usergroups.*`, `admin.users.*`, `admin.apps.*`) - Thanks stevengill seratch

**Updates**

1. [WebClient][RTMClient] Fixed a bunch of the currency issues this SDK had (429 463 492 497 530 558 569 605 613 619 626 630 631 633 669) - Thanks seratch aaguilartablada aoberoi stevengill
2. [WebClient] 681 560 Enable using bool values for request parameters - Thanks roman-kachanovsky seratch
3. [WebClient] 661 678 Improve handling of required "ids" parameters (e.g., channel_ids, users) - Thanks seratch
4. [WebClient] 680 Add non-conversation API deprecation warnings - Thanks seratch
5. [WebClient] 671 670 Enable passing None values for request parameters (they used to result in errors) - Thanks seratch
6. [WebClient] 673 Fix 672 files.upload fails with a filepath containing multi byte chars - Thanks yuji38kwmt seratch
7. [WebClient] 656 Fix 594 preview_image for files.remote.add API method is not properly supported - Thanks seratch
8. [Maintenance] 618 Add py.typed file to package distribution - Thanks JKillian
9. [WebClient] 599 Strip token string parameters of whitespace - Thanks TheFrozenFire

**New Features**

1. [WebClient] Adding new `oauth.v2.access` Web API method. 577

**New Features**

1. [WebClient] Adding new admin.* Web API methods. 571

**Updates**
1. [WebClient] We're no longer validating token types for Web API methods. Improves compatibility with granular bot permisisons. 568 (Thanks Smotko)
2. [WebClient] Correcting typos in descriptions 554 (Thanks phamk)
3. [WebClient] Fixed 'iteracting' typo in library file headers 564 (Thanks acabey)
4. [Message Builders] Remove value from LinkButtonElement 563 (Thanks pedroma)

**Updates**
1. [WebClient] Fixing a regression that causes the client to close sessions prematurely. 544 (Thanks fatih-acar!)
2. [WebClient] Adding required missing view param to `views.update` Web API method. 542

**New Features**

1. [WebClient] Adding new views.publish Web API method. 540

**Updates**

1. [WebClient] Some server responses don't return json. Correcting initial assumption. 540
2. [Maintenance] Add py.typed to mark the library to support type hinting 524

**Updates**
1. [Docs] Fix Indentation of Code Snippets in README.md 525 (Thanks abhishekjiitr)
2. [WebClient] Fix Web Client custom iterator 521 (Thanks smaeda-ks)
3. [WebClient] Oauth previously failed to pass along credentials properly. This is fixed now. 527
4. [WebClient] When a SlackApiError occurs we're now passing the entire SlackResponse into the exception. 527