handle manifest version logic, update manifest version to 2105

[NamanJain8]

The backward compatibility of the backup's manifest was broken by #7810, although the tool was added (#7815) that enables smooth migration of manifest.
This PR makes backup backward compatible, by updating the manifest(in-memory) after reading.

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This change is 

[manishrjain]

Reviewed 34 of 34 files at r1.
Reviewable status: all files reviewed, 5 unresolved discussions (waiting on @NamanJain8 and @vvbalaji-dgraph)

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ee/updatemanifest/run.go, line 126 at r1 (raw file):

	// Update the master manifest with the changes for drop operations and group predicates.
	for _, manifest := range masterManifest.Manifests {
		if manifest.Version == 2103 {

<= ??

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worker/backup_ee.go, line 551 at r1 (raw file):

	}

	manifest, err := GetManifestWithoutUpgrade(handler, uri)

GetManifestNoUpgrade

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worker/backup_manifest.go, line 169 at r1 (raw file):

func parseNsAttr(attr string) (uint64, string, error) {
	if strings.ContainsRune(attr, replacementRune) {
		return 0, "", errors.New("replacement char found")

Improve the error.

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worker/backup_manifest.go, line 225 at r1 (raw file):

		}
	case 2105:
		// pass

default case?

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worker/backup_manifest.go, line 266 at r1 (raw file):

// GetManifestWithoutUpgrade returns the master manifest using the given handler and uri.
func GetManifestWithoutUpgrade(h UriHandler, uri *url.URL) (*MasterManifest, error) {

GetManifestNoUpgrade

[NamanJain8]

Reviewed 26 of 34 files at r1.
Dismissed @manishrjain from 5 discussions.
Reviewable status: 30 of 34 files reviewed, all discussions resolved

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ee/updatemanifest/run.go, line 126 at r1 (raw file):

Previously, manishrjain (Manish R Jain) wrote…

<= ??

This is for a specific tool, so we need to check only for version 2103.

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worker/backup_ee.go, line 551 at r1 (raw file):

Previously, manishrjain (Manish R Jain) wrote…

GetManifestNoUpgrade

Done.

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worker/backup_manifest.go, line 169 at r1 (raw file):

Previously, manishrjain (Manish R Jain) wrote…

Improve the error.

Done.

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worker/backup_manifest.go, line 225 at r1 (raw file):

Previously, manishrjain (Manish R Jain) wrote…

default case?

2105 is the default case.

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worker/backup_manifest.go, line 266 at r1 (raw file):

Previously, manishrjain (Manish R Jain) wrote…

GetManifestNoUpgrade

Done.