Remove underscores from ECR docker versions

[achals]

Signed-off-by: Achal Shah achals@gmail.com

What this PR does / why we need it:
The initial assumption about ECR not supporting periods isn't true, so we should be able simplify some of the release logic. Also, the README was updated without updating the template, which this PR fixes.
Which issue(s) this PR fixes:

Fixes #2136

Does this PR introduce a user-facing change?:

none

[codecov-commenter]

Codecov Report

Merging #2139 (a036ab9) into master (37c0abe) will decrease coverage by 0.28%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2139      +/-   ##
==========================================
- Coverage   83.21%   82.92%   -0.29%     
==========================================
  Files         101      101              
  Lines        8162     8218      +56     
==========================================
+ Hits         6792     6815      +23     
- Misses       1370     1403      +33     

Flag	Coverage Δ
integrationtests	73.39% <ø> (-0.31%)	⬇️
unittests	57.92% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
sdk/python/feast/infra/online_stores/dynamodb.py	67.63% <0.00%> (-12.72%)	⬇️
sdk/python/feast/infra/utils/aws_utils.py	83.33% <0.00%> (-1.45%)	⬇️
.../integration/online_store/test_universal_online.py	97.67% <0.00%> (-0.47%)	⬇️
sdk/python/feast/infra/online_stores/datastore.py	93.70% <0.00%> (+2.36%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 37c0abe...a036ab9. Read the comment docs.

[felixwang9817]

/lgtm

[feast-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: achals, felixwang9817

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [achals,felixwang9817]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment