Set default wait to 30 minutes for eks cluster create

[gshaw-pivotal]

1. What this PR does / why we need it:

Standardizes the ready wait timeout for EKS cluster creation to 30 minutes.

Introduces 2 constants:

• a constant to hold the timeout in minutes (30)
• a constant to hold the timeout in nano seconds (the base time unit) and derives its value from the first constant To change the default timeout one only needs to change the value in the 'minutesBasedDefaultTimeout' constant.

Fixes logic in 'internal/resources/ekscluster/data_source.go' where if a user did not provide a 'ready_wait_timeout' key, or provided the value of 'default' it now sets the timeout to 30 minutes instead of 5 minutes.

2. Which issue(s) this PR fixes

Revisits Issue #181

3. Additional information

4. Special notes for your reviewer

[codecov-commenter]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (7922ec6) 25.69% compared to head (0d19538) 25.70%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #324 +/- ## ======================================= Coverage 25.69% 25.70% ======================================= Files 187 187 Lines 15775 15774 -1 ======================================= Hits 4054 4054 + Misses 11516 11515 -1 Partials 205 205 ``` | [Files](https://app.codecov.io/gh/vmware/terraform-provider-tanzu-mission-control/pull/324?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vmware) | Coverage Δ | | |---|---|---| | [...ternal/resources/ekscluster/resource\_ekscluster.go](https://app.codecov.io/gh/vmware/terraform-provider-tanzu-mission-control/pull/324?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vmware#diff-aW50ZXJuYWwvcmVzb3VyY2VzL2Vrc2NsdXN0ZXIvcmVzb3VyY2VfZWtzY2x1c3Rlci5nbw==) | `16.74% <0.00%> (ø)` | | | [internal/resources/ekscluster/data\_source.go](https://app.codecov.io/gh/vmware/terraform-provider-tanzu-mission-control/pull/324?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vmware#diff-aW50ZXJuYWwvcmVzb3VyY2VzL2Vrc2NsdXN0ZXIvZGF0YV9zb3VyY2UuZ28=) | `0.00% <0.00%> (ø)` | |

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